diff --git a/packages/hydrooj/src/entry/common.ts b/packages/hydrooj/src/entry/common.ts
index 10c27d29..46e6bd94 100644
--- a/packages/hydrooj/src/entry/common.ts
+++ b/packages/hydrooj/src/entry/common.ts
@@ -13,7 +13,7 @@ export const builtinLib = [
     'jwt', 'download', 'i18n', 'mail', 'useragent',
     'crypto', 'misc', 'paginate', 'hash.hydro', 'rank',
     'validator', 'ui', 'sysinfo', 'testdata.convert.ini', 'testdataConfig',
-    'content',
+    'content', 'difficulty',
 ];
 
 export const builtinModel = [
diff --git a/packages/hydrooj/src/handler/judge.ts b/packages/hydrooj/src/handler/judge.ts
index 7bfe7e61..15740eac 100644
--- a/packages/hydrooj/src/handler/judge.ts
+++ b/packages/hydrooj/src/handler/judge.ts
@@ -2,6 +2,7 @@ import { ObjectID } from 'mongodb';
 import { JudgeResultBody, Rdoc, TestCase } from '../interface';
 import { sleep } from '../utils';
 import { Logger } from '../logger';
+import difficultyAlgorithm from '../lib/difficulty';
 import * as record from '../model/record';
 import * as problem from '../model/problem';
 import * as builtin from '../model/builtin';
@@ -27,7 +28,11 @@ async function _postJudge(rdoc: Rdoc) {
             rdoc._id, rdoc.pid, accept, rdoc.score, rdoc.contest.type,
         );
     } else if (updated) await domain.incUserInDomain(rdoc.domainId, rdoc.uid, 'nAccept', 1);
-    if (accept && updated) await problem.inc(rdoc.domainId, rdoc.pid, 'nAccept', 1);
+    const pdoc = (accept && updated)
+        ? await problem.inc(rdoc.domainId, rdoc.pid, 'nAccept', 1)
+        : await problem.get(rdoc.domainId, rdoc.pid);
+    const difficulty = difficultyAlgorithm(pdoc.nSubmit, pdoc.nAccept);
+    await problem.edit(pdoc.domainId, pdoc.docId, { difficulty });
 }
 
 export async function next(body: JudgeResultBody) {
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index c3d39f8c..ea7e4906 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -10,6 +10,7 @@ import {
 } from '../interface';
 import paginate from '../lib/paginate';
 import { isTitle, isContent, isPid } from '../lib/validator';
+import difficultyAlgorithm from '../lib/difficulty';
 import * as system from '../model/system';
 import * as problem from '../model/problem';
 import * as record from '../model/record';
@@ -333,10 +334,10 @@ export class ProblemEditHandler extends ProblemManageHandler {
             title, content, pid: newPid, hidden, tag: tag ?? [],
         };
         let pdoc = await problem.get(domainId, pid);
+        $update.difficulty = difficultyAlgorithm(pdoc.nSubmit, pdoc.nAccept);
         await bus.serial('problem/before-edit', $update);
         pdoc = await problem.edit(domainId, pdoc.docId, $update);
         await bus.emit('problem/edit', pdoc);
-        await global.Hydro.script.difficulty.run({ domainId, pid }, console.log);
         this.response.redirect = this.url('problem_detail', { pid: newPid || pdoc.docId });
     }
 }
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index a5249db9..7392356c 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -520,6 +520,7 @@ interface GeoIP {
 
 export interface Lib extends Record<string, any> {
     download: typeof import('./lib/download'),
+    difficulty: typeof import('./lib/difficulty'),
     buildContent: typeof import('./lib/content').buildContent,
     'hash.hydro': typeof import('./lib/hash.hydro'),
     i18n: typeof import('./lib/i18n'),
diff --git a/packages/hydrooj/src/script/difficulty.ts b/packages/hydrooj/src/lib/difficulty.ts
similarity index 68%
rename from packages/hydrooj/src/script/difficulty.ts
rename to packages/hydrooj/src/lib/difficulty.ts
index b37615cb..219ee3ca 100644
--- a/packages/hydrooj/src/script/difficulty.ts
+++ b/packages/hydrooj/src/lib/difficulty.ts
@@ -1,7 +1,3 @@
-import * as problem from '../model/problem';
-
-export const description = 'Caculate the difficulty of a problem';
-
 const _CACHE_INFO = {
     last_s: 0.0,
     last_y: 0,
@@ -46,17 +42,5 @@ function difficultyAlgorithm(nSubmit: number, nAccept: number) {
     return Math.max(ans, 1);
 }
 
-export async function run({
-    domainId, pid,
-}) {
-    const pdoc = await problem.get(domainId, pid);
-    const difficulty = difficultyAlgorithm(pdoc.nSubmit, pdoc.nAccept);
-    return await problem.edit(domainId, pdoc.docId, { difficulty });
-}
-
-export const validate = {
-    domainId: { $type: 'string' },
-    pid: { $type: 'number' },
-};
-
-global.Hydro.script.difficulty = { run, description, validate };
+export = difficultyAlgorithm;
+global.Hydro.lib.difficulty = difficultyAlgorithm;
diff --git a/packages/hydrooj/src/script/problemStat.ts b/packages/hydrooj/src/script/problemStat.ts
index aeb958e1..02d01986 100644
--- a/packages/hydrooj/src/script/problemStat.ts
+++ b/packages/hydrooj/src/script/problemStat.ts
@@ -29,7 +29,7 @@ export async function udoc() {
     ];
     let bulk = db.collection('domain.user').initializeUnorderedBulkOp();
     const cursor = db.collection('record').aggregate(pipeline);
-    while (cursor.hasNext()) {
+    while (await cursor.hasNext()) {
         const adoc = await cursor.next() as any;
         bulk.find({
             domainId: adoc._id.domainId,
diff --git a/packages/hydrooj/src/upgrade.ts b/packages/hydrooj/src/upgrade.ts
index 35f33e3a..55c31c62 100644
--- a/packages/hydrooj/src/upgrade.ts
+++ b/packages/hydrooj/src/upgrade.ts
@@ -15,6 +15,7 @@ import * as problem from './model/problem';
 import * as domain from './model/domain';
 import * as document from './model/document';
 import * as system from './model/system';
+import difficultyAlgorithm from './lib/difficulty';
 
 const logger = new Logger('upgrade');
 type UpgradeScript = () => Promise<boolean | void>;
@@ -201,11 +202,20 @@ const scripts: UpgradeScript[] = [
         return true;
     },
     // Set null tag to []
-    async function _9_10() {
+    async function _10_11() {
         const _FRESH_INSTALL_IGNORE = 1;
         await db.collection('document').updateMany({ docType: 10, tag: null }, { $set: { tag: [] } });
         return true;
     },
+    // Update problem difficulty
+    async function _11_12() {
+        const _FRESH_INSTALL_IGNORE = 1;
+        await iterateAllProblem(['nSubmit', 'nAccept'], async (pdoc) => {
+            const difficulty = difficultyAlgorithm(pdoc.nSubmit, pdoc.nAccept);
+            await problem.edit(pdoc.domainId, pdoc.docId, { difficulty });
+        });
+        return true;
+    },
 ];
 
 export = scripts;