diff --git a/packages/hydrooj/locales/zh.yaml b/packages/hydrooj/locales/zh.yaml
index a9cd1c81b..4bb7f3da0 100644
--- a/packages/hydrooj/locales/zh.yaml
+++ b/packages/hydrooj/locales/zh.yaml
@@ -437,6 +437,7 @@ List View: 列表视图
 Live: 正在进行
 Live...: 正在进行…
 Location: 位置
+Lock Topic: 锁定主题
 Login to Attend Contest: 登录后参加比赛
 Login to Claim Homework: 登录后认领作业
 Login to Create a Discussion: 登录后创建讨论
@@ -750,6 +751,7 @@ Terms of Service: 服务条款
 Test data comes from: 测试数据来自
 Testdata Config: 测试数据配置
 Text: 文本
+The discussion is locked, you can not reply anymore.: 此讨论已经锁定，您不能再回复。
 The homework's deadline is due but in extension. You can still submit for this problem but your score will be penalized.: 作业已超过截止时间，但仍在延期时间内。您递交题目将无法获得全部分数。
 The invitation code to enter to successfully join the domain. You can only use letters and numbers in the code and it should not be longer than 64 characters.: 加入此域的邀请码。您只能使用字母和数字，并且不能长于 64 个字符。
 The invitation code you provided is invalid.: 您提供的邀请码无效。
@@ -800,6 +802,7 @@ Unhide Selected: 取消隐藏选中
 Unique: 唯一
 Unknown field {0}.: 未知字段 {0}。
 Unknown: 未知
+Unlock Topic: 解锁主题
 Unordered List: 无序列表
 Unsaved session expire seconds: 未保存的会话的过期秒数
 Unstar Topic: 取消收藏
diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 0374718f9..def6ca832 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "3.4.24",
+    "version": "3.4.25",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",
diff --git a/packages/hydrooj/src/error.ts b/packages/hydrooj/src/error.ts
index 44d764584..1802cb1b7 100644
--- a/packages/hydrooj/src/error.ts
+++ b/packages/hydrooj/src/error.ts
@@ -98,6 +98,7 @@ export const DomainJoinForbiddenError = Err('DomainJoinForbiddenError', Forbidde
 export const DomainJoinAlreadyMemberError = Err('DomainJoinAlreadyMemberError', ForbiddenError, 'Failed to join the domain. You are already a member.');
 export const InvalidJoinInvitationCodeError = Err('InvalidJoinInvitationCodeError', ForbiddenError, 'The invitation code you provided is invalid.');
 export const CurrentPasswordError = Err('CurrentPasswordError', ForbiddenError, "Current password doesn't match.");
+export const DiscussionLockedError = Err('DiscussionLockedError', ForbiddenError, 'The discussion is locked, you can not reply anymore.');
 
 export const UserNotFoundError = Err('UserNotFoundError', NotFoundError, 'User {0} not found.');
 export const NoProblemError = Err('NoProblemError', NotFoundError, 'No problem.');
diff --git a/packages/hydrooj/src/handler/discussion.ts b/packages/hydrooj/src/handler/discussion.ts
index 08d0a5783..133baff12 100644
--- a/packages/hydrooj/src/handler/discussion.ts
+++ b/packages/hydrooj/src/handler/discussion.ts
@@ -1,6 +1,9 @@
 import { isSafeInteger } from 'lodash';
 import { ObjectID } from 'mongodb';
-import { DiscussionNotFoundError, DocumentNotFoundError, PermissionError } from '../error';
+import {
+    DiscussionLockedError, DiscussionNotFoundError, DocumentNotFoundError,
+    PermissionError,
+} from '../error';
 import { DiscussionDoc, DiscussionReplyDoc, DiscussionTailReplyDoc } from '../interface';
 import paginate from '../lib/paginate';
 import { PERM, PRIV } from '../model/builtin';
@@ -207,6 +210,14 @@ class DiscussionDetailHandler extends DiscussionHandler {
         this.checkPriv(PRIV.PRIV_USER_PROFILE);
     }
 
+    @param('did', Types.ObjectID)
+    @param('lock', Types.Boolean)
+    async postSetLock(domainId: string, did: ObjectID, lock: boolean) {
+        if (!this.user.own(this.ddoc)) this.checkPerm(PERM.PERM_LOCK_DISCUSSION);
+        await discussion.edit(domainId, did, { lock });
+        this.back();
+    }
+
     @param('type', Types.Range(['did', 'drid']))
     @param('id', Types.ObjectID)
     @param('emoji', Types.Emoji)
@@ -223,6 +234,7 @@ class DiscussionDetailHandler extends DiscussionHandler {
     @param('content', Types.Content)
     async postReply(domainId: string, did: ObjectID, content: string) {
         this.checkPerm(PERM.PERM_REPLY_DISCUSSION);
+        if (this.ddoc.lock) throw new DiscussionLockedError(domainId, did);
         await this.limitRate('add_discussion', 3600, 60);
         const targets = new Set(Array.from(content.matchAll(/@\[\]\(\/user\/(\d+)\)/g)).map((i) => +i[1]));
         const uids = Object.keys(await user.getList(domainId, Array.from(targets))).map((i) => +i);
@@ -241,6 +253,7 @@ class DiscussionDetailHandler extends DiscussionHandler {
     @param('content', Types.Content)
     async postTailReply(domainId: string, drid: ObjectID, content: string) {
         this.checkPerm(PERM.PERM_REPLY_DISCUSSION);
+        if (this.ddoc.lock) throw new DiscussionLockedError(domainId, this.ddoc.docId);
         await this.limitRate('add_discussion', 3600, 60);
         const targets = new Set(Array.from(content.matchAll(/@\[\]\(\/user\/(\d+)\)/g)).map((i) => +i[1]));
         const uids = Object.keys(await user.getList(domainId, Array.from(targets))).map((i) => +i);
@@ -355,7 +368,9 @@ class DiscussionEditHandler extends DiscussionHandler {
         if (!this.user.hasPerm(PERM.PERM_HIGHLIGHT_DISCUSSION)) highlight = this.ddoc.highlight;
         if (!this.user.hasPerm(PERM.PERM_PIN_DISCUSSION)) pin = this.ddoc.pin;
         await Promise.all([
-            discussion.edit(domainId, did, title, content, highlight, pin),
+            discussion.edit(domainId, did, {
+                title, content, highlight, pin,
+            }),
             oplog.log(this, 'discussion.edit', this.ddoc),
         ]);
         this.response.body = { did };
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 8571cbf0d..d64fe694b 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -435,6 +435,7 @@ declare module './model/discussion' {
         react: Record<string, number>;
         sort: number;
         lastRCount: number;
+        lock?: boolean;
     }
 }
 
diff --git a/packages/hydrooj/src/model/builtin.ts b/packages/hydrooj/src/model/builtin.ts
index 8807bda44..a54039fe2 100644
--- a/packages/hydrooj/src/model/builtin.ts
+++ b/packages/hydrooj/src/model/builtin.ts
@@ -58,6 +58,7 @@ export const PERM = {
     PERM_DELETE_DISCUSSION_REPLY: 1n << 38n,
     PERM_DELETE_DISCUSSION_REPLY_SELF: 1n << 39n,
     PERM_DELETE_DISCUSSION_REPLY_SELF_DISCUSSION: 1n << 40n,
+    PERM_LOCK_DISCUSSION: 64n,
 
     // Contest
     PERM_VIEW_CONTEST: 1n << 41n,
@@ -131,6 +132,7 @@ export const PERMS = [
     Permission('perm_discussion', PERM.PERM_PIN_DISCUSSION, 'Pin discussions'),
     Permission('perm_discussion', PERM.PERM_EDIT_DISCUSSION, 'Edit discussions'),
     Permission('perm_discussion', PERM.PERM_EDIT_DISCUSSION_SELF, 'Edit own discussions'),
+    Permission('perm_discussion', PERM.PERM_LOCK_DISCUSSION, 'Lock discussions'),
     Permission('perm_discussion', PERM.PERM_DELETE_DISCUSSION, 'Delete discussions'),
     Permission('perm_discussion', PERM.PERM_DELETE_DISCUSSION_SELF, 'Delete own discussions'),
     Permission('perm_discussion', PERM.PERM_REPLY_DISCUSSION, 'Reply discussions'),
diff --git a/packages/hydrooj/src/model/discussion.ts b/packages/hydrooj/src/model/discussion.ts
index b616da22c..f30939123 100644
--- a/packages/hydrooj/src/model/discussion.ts
+++ b/packages/hydrooj/src/model/discussion.ts
@@ -57,6 +57,7 @@ export const PROJECTION_LIST: DiscussionDoc.Field[] = [
 ];
 export const PROJECTION_PUBLIC: DiscussionDoc.Field[] = [
     ...PROJECTION_LIST, 'content', 'history', 'react', 'maintainer',
+    'lock',
 ];
 
 export const typeDisplay = {
@@ -103,14 +104,8 @@ export async function get<T extends DiscussionDoc.Field>(
     return await document.get(domainId, document.TYPE_DISCUSSION, did, projection);
 }
 
-export function edit(
-    domainId: string, did: ObjectID,
-    title: string, content: string, highlight: boolean, pin: boolean,
-): Promise<DiscussionDoc | null> {
-    const payload = {
-        title, content, highlight, pin,
-    };
-    return document.set(domainId, document.TYPE_DISCUSSION, did, payload);
+export function edit(domainId: string, did: ObjectID, $set: Partial<DiscussionDoc>) {
+    return document.set(domainId, document.TYPE_DISCUSSION, did, $set);
 }
 
 export function inc(
diff --git a/packages/hydrooj/src/model/message.ts b/packages/hydrooj/src/model/message.ts
index 51684079f..26a8ce57b 100644
--- a/packages/hydrooj/src/model/message.ts
+++ b/packages/hydrooj/src/model/message.ts
@@ -26,7 +26,7 @@ class MessageModel {
             from, to, content, _id: res.insertedId, flag,
         };
         if (from !== to) bus.broadcast('user/message', to, mdoc);
-        await user.inc(to, 'unreadMsg', 1);
+        if (flag & MessageModel.FLAG_UNREAD) await user.inc(to, 'unreadMsg', 1);
         return mdoc;
     }
 
diff --git a/packages/ui-default/package.json b/packages/ui-default/package.json
index 056981b29..f873e0488 100644
--- a/packages/ui-default/package.json
+++ b/packages/ui-default/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@hydrooj/ui-default",
-  "version": "4.31.13",
+  "version": "4.31.14",
   "author": "undefined <i@undefined.moe>",
   "license": "AGPL-3.0",
   "main": "hydro.js",
diff --git a/packages/ui-default/templates/components/comments_discussion.html b/packages/ui-default/templates/components/comments_discussion.html
index 4d760ccba..8dd20b4cd 100644
--- a/packages/ui-default/templates/components/comments_discussion.html
+++ b/packages/ui-default/templates/components/comments_discussion.html
@@ -34,7 +34,8 @@
   reply_edit_text = 'Update',
   comment_delete_op = 'delete_reply',
   reply_delete_op = 'delete_tail_reply',
-  reactions = {}
+  reactions = {},
+  ddoc = {}
 ) %}
 <ul class="dczcomments__list view--discussion">
 {% if handler.user.hasPerm(comment_post_perm) %}
@@ -44,6 +45,9 @@
       <img src="{{ avatarUrl(handler.user.avatar, 60) }}" width="60" height="60" class="medium user-profile-avatar">
     </div>
     <div class="media__body top">
+      {% if ddoc.lock %}
+        <textarea class="textbox" name="dczcomments__dummy-box" readonly placeholder="{{ _('The discussion is locked, you can not reply anymore.') }}"></textarea>
+      {% else %}
       <div class="hasjs--hide">
         <form method="post" class="dczcomments__box" name="dczcomments__box__form" data-hotkey="ctrl+enter:submit,esc:vjCommentBoxCancel">
           <div>
@@ -73,6 +77,7 @@
           </div>
         </li>
       </ul>
+      {% endif %}
     </div>
   </div>
 </li>
diff --git a/packages/ui-default/templates/discussion_detail.html b/packages/ui-default/templates/discussion_detail.html
index e2ec4778d..8185ab2cd 100644
--- a/packages/ui-default/templates/discussion_detail.html
+++ b/packages/ui-default/templates/discussion_detail.html
@@ -45,6 +45,16 @@
             <span class="starred--show"><span class="icon icon-star"></span> {{ _('Unstar Topic') }}</span>
           </button>
         </form></li>
+      {% endif %}
+      {% if handler.user.own(ddoc) or handler.user.hasPerm(perm.PERM_LOCK_DISCUSSION) %}
+        <li><form class="form--inline" method="post">
+          <input type="hidden" name="operation" value="set_lock">
+          {% if not ddoc.lock %}<input type="hidden" name="lock" value="1">{% endif %}
+          <button class="star{% if ddoc.lock %} activated{% endif %}" type="submit">
+            <span class="starred--hide">{{ _('Lock Topic') }}</span>
+            <span class="starred--show">{{ _('Unlock Topic') }}</span>
+          </button>
+        </form></li>
       {% endif %}
         <li><a href="{{ url('wiki_help', anchor='contact') }}">
           <span class="icon icon-warning"></span> {{ _('Report') }}
@@ -78,7 +88,8 @@
           reply_delete_perm = perm.PERM_DELETE_DISCUSSION_REPLY_SELF_DISCUSSION if handler.user.own(ddoc) else perm.PERM_DELETE_DISCUSSION_REPLY,
           reply_edit_self_perm = perm.PERM_EDIT_DISCUSSION_REPLY_SELF,
           reply_delete_self_perm = perm.PERM_DELETE_DISCUSSION_REPLY_SELF,
-          reactions = reactions
+          reactions = reactions,
+          ddoc = ddoc
         ) }}
         {{ paginator.render(page, pcount) }}
       {% if drcount == 0 %}
@@ -97,9 +108,7 @@
             <img src="{{ avatarUrl(udoc.avatar, 80) }}" width="80" height="80" class="medium user-profile-avatar">
           </div>
           <div class="media__body">
-            <p>
-              {{ user.render_inline(udoc, avatar=false, modbadge=false) }}
-            </p>
+            <p>{{ user.render_inline(udoc, avatar=false, modbadge=false) }}</p>
           </div>
         </div>
       </div>