diff --git a/application/common/service/SplitRedirectService.php b/application/common/service/SplitRedirectService.php
index 86c3af3..09f9db5 100755
--- a/application/common/service/SplitRedirectService.php
+++ b/application/common/service/SplitRedirectService.php
@@ -195,7 +195,8 @@ class SplitRedirectService
 
         $keys = array_keys($groups);
         if (count($keys) === 1) {
-            return $keys[0];
+            // PHP 会把纯数字字符串键转成 int，需强转以匹配 ?string 返回类型
+            return (string) $keys[0];
         }
 
         $r = random_int(1, $total);
@@ -203,11 +204,11 @@ class SplitRedirectService
         foreach ($groups as $key => $rows) {
             $acc += count($rows);
             if ($r <= $acc) {
-                return $key;
+                return (string) $key;
             }
         }
 
-        return $keys[0];
+        return (string) $keys[0];
     }
 
     /**
diff --git a/patches/application/common/service/SplitRedirectService.php b/patches/application/common/service/SplitRedirectService.php
index 86c3af3..09f9db5 100755
--- a/patches/application/common/service/SplitRedirectService.php
+++ b/patches/application/common/service/SplitRedirectService.php
@@ -195,7 +195,8 @@ class SplitRedirectService
 
         $keys = array_keys($groups);
         if (count($keys) === 1) {
-            return $keys[0];
+            // PHP 会把纯数字字符串键转成 int，需强转以匹配 ?string 返回类型
+            return (string) $keys[0];
         }
 
         $r = random_int(1, $total);
@@ -203,11 +204,11 @@ class SplitRedirectService
         foreach ($groups as $key => $rows) {
             $acc += count($rows);
             if ($r <= $acc) {
-                return $key;
+                return (string) $key;
             }
         }
 
-        return $keys[0];
+        return (string) $keys[0];
     }
 
     /**