diff --git a/resources/views/business/pages/financial-rules/account-mapping.blade.php b/resources/views/business/pages/financial-rules/account-mapping.blade.php
index d312904f..3b313c61 100644
--- a/resources/views/business/pages/financial-rules/account-mapping.blade.php
+++ b/resources/views/business/pages/financial-rules/account-mapping.blade.php
@@ -103,11 +103,21 @@
         /* 表格必须锁列宽（table-layout:fixed）。默认的自动列宽会按内容互相挤压，
            「借方/贷方科目」两列会被挤到文字被截断；锁死后按上面 th 的宽度分配，
            窗口不够宽时由外层 .upstream-data-table-scroll 横向滚动。
-           87.5rem = 各列宽度之和，改列宽时要一起改。 */
-        .am-table { table-layout: fixed; min-width: 87.5rem; }
+           89rem = 各列宽度之和，改列宽时要一起改。 */
+        .am-table { table-layout: fixed; min-width: 89rem; }
         /* 只读单元格超长就省略号（编辑态那格要放开，否则下拉会被裁） */
         .am-table > tbody > tr.am-item:not(.is-editing) > td { overflow: hidden; text-overflow: ellipsis; }
 
+        /* 序号列：3.5rem 才放得下三位数，居中并锁死数字等宽，
+           避免宽窗口下被按比例挤压后出现「1…」 */
+        .am-table .am-index {
+            width: 3.5rem;
+            min-width: 3.5rem;
+            max-width: 3.5rem;
+            text-align: center;
+            font-variant-numeric: tabular-nums;
+        }
+
         /* 行内编辑 */
         /* 注意：td 上有 height:2.5rem + white-space:nowrap（来自 upstream-data-table），
            编辑态必须放开，否则一级/二级两个下拉会被压成一行、挤出单元格 */
@@ -324,7 +334,7 @@
             <table class="upstream-data-table am-table">
                 <thead>
                     <tr>
-                        <th style="width:2.5rem;">#</th>
+                        <th class="am-index" style="width:3.5rem;">序号</th>
                         <th style="width:4.5rem;">平台</th>
                         <th style="width:17rem;">账单项目</th>
                         <th style="width:12rem;">财务备注</th>
@@ -492,7 +502,7 @@
         var edit = (editingId === r.id && draft);
         if (edit) {
             return '<tr class="am-item is-editing" data-id="' + r.id + '">'
-                + '<td>' + (index + 1) + '</td>'
+                + '<td class="am-index">' + (index + 1) + '</td>'
                 + '<td class="am-edit-cell"><input data-f="platform" value="' + esc(draft.platform) + '" list="amPlatformList"></td>'
                 + '<td class="am-edit-cell"><input data-f="item" value="' + esc(draft.item) + '"></td>'
                 + '<td class="am-edit-cell"><input data-f="memo" value="' + esc(draft.memo) + '"></td>'
@@ -508,7 +518,7 @@
                 + '</div></td></tr>';
         }
         return '<tr class="am-item" data-id="' + r.id + '" data-index="' + index + '">'
-            + '<td>' + (index + 1) + '</td>'
+            + '<td class="am-index">' + (index + 1) + '</td>'
             + '<td>' + esc(r.platform) + '</td>'
             + '<td><span class="am-caret">▶</span> <span title="' + esc(r.item) + '">' + esc(r.item) + '</span></td>'
             + '<td><span title="' + esc(r.memo) + '">' + esc(r.memo) + '</span></td>'
diff --git a/tests/Feature/Business/AccountMappingPageTest.php b/tests/Feature/Business/AccountMappingPageTest.php
index 460f6da2..f094228c 100644
--- a/tests/Feature/Business/AccountMappingPageTest.php
+++ b/tests/Feature/Business/AccountMappingPageTest.php
@@ -95,6 +95,8 @@ class AccountMappingPageTest extends FeatureTestCase
             ->assertSee('var ROWS = [', false)
             ->assertSee('"platform":"得物"', false)
             ->assertSeeText('科目映射表')
+            // 序号列表头固定为「序号」且宽度 3.5rem：2.5rem 时三位数会被省略号截成「1…」
+            ->assertSee('class="am-index" style="width:3.5rem;">序号</th>', false)
             // ENDPOINT 经 @json 输出，斜杠会被转义成 \/，所以只断言变量名
             ->assertSee('var ENDPOINT =', false);
     }