diff --git a/packages/core/src/config.ts b/packages/core/src/config.ts
index b8c929741..a302a7ff3 100644
--- a/packages/core/src/config.ts
+++ b/packages/core/src/config.ts
@@ -660,7 +660,17 @@ export async function composeCreateRsbuildConfig(
 
     return {
       format: libConfig.format!,
+      // The merge order represents the priority of the configuration
+      // The priorities from high to low are as follows:
+      // 1 - userConfig: users can configure any Rsbuild and Rspack config
+      // 2 - libRsbuildConfig: the configuration that we compose from Rslib unique config and userConfig from 1
+      // 3 - internalRsbuildConfig: the built-in best practice Rsbuild configuration we provide in Rslib
+      // We should state in the document that the built-in configuration should not be changed optionally
+      // In compose process of 2, we may read some config from 1, and reassemble the related config,
+      // so before final mergeRsbuildConfig, we reset some specified fields
       config: mergeRsbuildConfig(
+        internalRsbuildConfig,
+        libRsbuildConfig,
         omitDeep(userConfig, [
           'bundle',
           'format',
@@ -669,10 +679,6 @@ export async function composeCreateRsbuildConfig(
           'syntax',
           'dts',
         ]),
-        libRsbuildConfig,
-        // Merge order matters, keep `internalRsbuildConfig` at the last position
-        // to ensure that the internal config is not overridden by user's config.
-        internalRsbuildConfig,
       ),
     };
   });
diff --git a/packages/core/tests/__snapshots__/config.test.ts.snap b/packages/core/tests/__snapshots__/config.test.ts.snap
index f975d2197..8955e14f1 100644
--- a/packages/core/tests/__snapshots__/config.test.ts.snap
+++ b/packages/core/tests/__snapshots__/config.test.ts.snap
@@ -59,6 +59,40 @@ exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1
       "tools": {
         "htmlPlugin": false,
         "rspack": [
+          {
+            "experiments": {
+              "rspackFuture": {
+                "bundlerInfo": {
+                  "force": false,
+                },
+              },
+            },
+            "optimization": {
+              "moduleIds": "named",
+            },
+            "resolve": {
+              "extensionAlias": {
+                ".cjs": [
+                  ".cts",
+                  ".cjs",
+                ],
+                ".js": [
+                  ".ts",
+                  ".tsx",
+                  ".js",
+                  ".jsx",
+                ],
+                ".jsx": [
+                  ".tsx",
+                  ".jsx",
+                ],
+                ".mjs": [
+                  ".mts",
+                  ".mjs",
+                ],
+              },
+            },
+          },
           {
             "experiments": {
               "outputModule": true,
@@ -89,35 +123,11 @@ exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1
             ],
           },
           {
-            "experiments": {
-              "rspackFuture": {
-                "bundlerInfo": {
-                  "force": false,
-                },
-              },
-            },
-            "optimization": {
-              "moduleIds": "named",
-            },
             "resolve": {
               "extensionAlias": {
-                ".cjs": [
-                  ".cts",
-                  ".cjs",
-                ],
                 ".js": [
                   ".ts",
                   ".tsx",
-                  ".js",
-                  ".jsx",
-                ],
-                ".jsx": [
-                  ".tsx",
-                  ".jsx",
-                ],
-                ".mjs": [
-                  ".mts",
-                  ".mjs",
                 ],
               },
             },
@@ -185,22 +195,6 @@ exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1
       "tools": {
         "htmlPlugin": false,
         "rspack": [
-          {
-            "externalsType": "commonjs",
-            "output": {
-              "chunkFormat": "commonjs",
-              "iife": false,
-              "library": {
-                "type": "commonjs",
-              },
-            },
-          },
-          [Function],
-          {
-            "target": [
-              "web",
-            ],
-          },
           {
             "experiments": {
               "rspackFuture": {
@@ -235,6 +229,32 @@ exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1
               },
             },
           },
+          {
+            "externalsType": "commonjs",
+            "output": {
+              "chunkFormat": "commonjs",
+              "iife": false,
+              "library": {
+                "type": "commonjs",
+              },
+            },
+          },
+          [Function],
+          {
+            "target": [
+              "web",
+            ],
+          },
+          {
+            "resolve": {
+              "extensionAlias": {
+                ".js": [
+                  ".ts",
+                  ".tsx",
+                ],
+              },
+            },
+          },
         ],
       },
     },
@@ -294,20 +314,6 @@ exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1
       "tools": {
         "htmlPlugin": false,
         "rspack": [
-          {
-            "externalsType": "umd",
-            "output": {
-              "library": {
-                "type": "umd",
-              },
-            },
-          },
-          [Function],
-          {
-            "target": [
-              "web",
-            ],
-          },
           {
             "experiments": {
               "rspackFuture": {
@@ -342,6 +348,30 @@ exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1
               },
             },
           },
+          {
+            "externalsType": "umd",
+            "output": {
+              "library": {
+                "type": "umd",
+              },
+            },
+          },
+          [Function],
+          {
+            "target": [
+              "web",
+            ],
+          },
+          {
+            "resolve": {
+              "extensionAlias": {
+                ".js": [
+                  ".ts",
+                  ".tsx",
+                ],
+              },
+            },
+          },
         ],
       },
     },
diff --git a/packages/core/tests/config.test.ts b/packages/core/tests/config.test.ts
index a0cd842ac..f099c72ed 100644
--- a/packages/core/tests/config.test.ts
+++ b/packages/core/tests/config.test.ts
@@ -178,7 +178,15 @@ describe('Should compose create Rsbuild config correctly', () => {
       },
       output: {
         filenameHash: false,
-        minify: true,
+      },
+      tools: {
+        rspack: {
+          resolve: {
+            extensionAlias: {
+              '.js': ['.ts', '.tsx'],
+            },
+          },
+        },
       },
     };
     const composedRsbuildConfig = await composeCreateRsbuildConfig(