diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 4d753ccd6..cf22342e6 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.29.23",
+    "version": "2.29.24",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index 5dff3a915..8824d46d2 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -4,7 +4,7 @@ import AdmZip from 'adm-zip';
 import { Time } from '@hydrooj/utils/lib/utils';
 import {
     ContestNotLiveError, ValidationError, ProblemNotFoundError,
-    ContestNotAttendedError, PermissionError, BadRequestError, ContestNotFoundError,
+    ContestNotAttendedError, PermissionError, BadRequestError, ContestNotFoundError, InvalidTokenError,
 } from '../error';
 import { ProblemDoc, Tdoc, User } from '../interface';
 import paginate from '../lib/paginate';
@@ -86,9 +86,11 @@ export class ContestDetailHandler extends Handler {
     }
 
     @param('tid', Types.ObjectID)
-    async postAttend(domainId: string, tid: ObjectID) {
+    @param('code', Types.String, true)
+    async postAttend(domainId: string, tid: ObjectID, code = '') {
         const tdoc = await contest.get(domainId, tid);
         if (contest.isDone(tdoc)) throw new ContestNotLiveError(tid);
+        if (tdoc._code && code !== tdoc._code) throw new InvalidTokenError(code);
         await contest.attend(domainId, tid, this.user._id);
         this.back();
     }
@@ -215,9 +217,10 @@ export class ContestEditHandler extends Handler {
     @param('rule', Types.Range(contest.RULES))
     @param('pids', Types.Content)
     @param('rated', Types.Boolean)
+    @param('code', Types.String, true)
     async post(
         domainId: string, tid: ObjectID, beginAtDate: string, beginAtTime: string, duration: number,
-        title: string, content: string, rule: string, _pids: string, rated = false,
+        title: string, content: string, rule: string, _pids: string, rated = false, _code = '',
     ) {
         const pids = _pids.replace(/，/g, ',').split(',').map((i) => {
             i = i.trim();
@@ -241,6 +244,7 @@ export class ContestEditHandler extends Handler {
         } else {
             tid = await contest.add(domainId, title, content, this.user._id, rule, beginAt, endAt, pids, rated);
         }
+        await contest.edit(domainId, tid, { _code });
         this.response.body = { tid };
         this.response.redirect = this.url('contest_detail', { tid });
     }
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 8a68d9d76..45f481770 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -321,6 +321,7 @@ export interface Tdoc<docType = document['TYPE_CONTEST'] | document['TYPE_HOMEWO
     rule: string,
     pids: ProblemId[],
     rated?: boolean,
+    _code?: string,
 
     // For homework
     penaltySince?: Date,
diff --git a/packages/ui-default/components/contest/contest.page.js b/packages/ui-default/components/contest/contest.page.js
new file mode 100644
index 000000000..ed8c13981
--- /dev/null
+++ b/packages/ui-default/components/contest/contest.page.js
@@ -0,0 +1,24 @@
+import { AutoloadPage } from 'vj/misc/Page';
+import delay from 'vj/utils/delay';
+import i18n from 'vj/utils/i18n';
+import request from 'vj/utils/request';
+import Notification from 'vj/components/notification';
+
+const contestPage = new AutoloadPage('contestPage', () => {
+    $('[data-contest-code]').on('click', (ev) => {
+        ev.preventDefault();
+        // eslint-disable-next-line no-alert
+        const code = prompt(i18n('Invitation code:'));
+        request.post('', {
+            operation: 'attend',
+            code,
+        }).then(() => {
+            Notification.success(i18n('Successfully attended'));
+            delay(1000).then(() => window.location.reload());
+        }).catch((e) => {
+            Notification.error(e.message || e);
+        });
+    });
+});
+
+export default contestPage;
diff --git a/packages/ui-default/package.json b/packages/ui-default/package.json
index 089425479..bcbdc5d0a 100644
--- a/packages/ui-default/package.json
+++ b/packages/ui-default/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@hydrooj/ui-default",
-  "version": "4.12.19",
+  "version": "4.12.20",
   "author": "undefined <i@undefined.moe>",
   "license": "AGPL-3.0",
   "main": "hydro.js",
diff --git a/packages/ui-default/templates/contest_edit.html b/packages/ui-default/templates/contest_edit.html
index 0e7f60f78..29edee899 100644
--- a/packages/ui-default/templates/contest_edit.html
+++ b/packages/ui-default/templates/contest_edit.html
@@ -7,7 +7,7 @@
         <form method="post">
           <div class="row">
             {{ form.form_select({
-                 columns:4,
+                 columns:3,
                  label:'Rule',
                  name:'rule',
                  options:rules,
@@ -23,8 +23,16 @@
                  autofocus:true,
                  row:false
                }) }}
+            {{ form.form_text({
+                 columns:3,
+                 label:'Invitation code',
+                 name:'code',
+                 placeholder:_('(leave blank if none)'),
+                 value:tdoc.code|default(''),
+                 row:false
+               }) }}
             {{ form.form_checkbox({
-                columns:4,
+                columns:2,
                 label:'Rated',
                 name:'rated',
                 placeholder:_('Is rated'),
diff --git a/packages/ui-default/templates/partials/contest_sidebar.html b/packages/ui-default/templates/partials/contest_sidebar.html
index d79533c0b..1c3ce9648 100644
--- a/packages/ui-default/templates/partials/contest_sidebar.html
+++ b/packages/ui-default/templates/partials/contest_sidebar.html
@@ -41,13 +41,13 @@
     {% if not attended and not model.contest.isDone(tdoc) %}
       <li class="menu__item">
     {% if handler.user.hasPerm(perm.PERM_ATTEND_CONTEST) and handler.user.hasPriv(PRIV.PRIV_USER_PROFILE) %}
-        <form action="{{ url('contest_detail', tid=tdoc.docId) }}" method="POST">
-          <input type="hidden" name="operation" value="attend">
-          <input type="hidden" name="csrfToken" value="{{ handler.csrfToken }}">
-          <button class="menu__link" type="submit">
-            <span class="icon icon-add"></span> {{ _('Attend Contest') }}
-          </button>
-        </form>
+      <form action="{{ url('contest_detail', tid=tdoc.docId) }}" method="POST">
+        <input type="hidden" name="operation" value="attend">
+        <input type="hidden" name="csrfToken" value="{{ handler.csrfToken }}">
+        <button class="menu__link" {% if tdoc._code %}data-contest-code{% endif %} type="submit">
+          <span class="icon icon-add"></span> {{ _('Attend Contest') }}
+        </button>
+      </form>
     {% elif not handler.user.hasPriv(PRIV.PRIV_USER_PROFILE) %}
         <a class="menu__link" href="javascript:showSignInDialog()">
           <span class="icon icon-add"></span> {{ _('Login to Attend Contest') }}