diff --git a/src/EasyAbp.FileManagement.EntityFrameworkCore/EasyAbp/FileManagement/Files/FileRepository.cs b/src/EasyAbp.FileManagement.EntityFrameworkCore/EasyAbp/FileManagement/Files/FileRepository.cs
index 83e2edb..1710bdb 100644
--- a/src/EasyAbp.FileManagement.EntityFrameworkCore/EasyAbp/FileManagement/Files/FileRepository.cs
+++ b/src/EasyAbp.FileManagement.EntityFrameworkCore/EasyAbp/FileManagement/Files/FileRepository.cs
@@ -120,11 +120,11 @@ public virtual async Task<string> GetFileNameWithNextSerialNumberAsync(string fi
             var nextNumber =
                 fileNames
                     .Select(x =>
-                        x.Substring(part1.Length, x.LastIndexOf(part2, StringComparison.Ordinal) - part1.Length))
+                        x.LastIndexOf(part2, StringComparison.Ordinal) > 0 ? x.Substring(part1.Length, x.LastIndexOf(part2, StringComparison.Ordinal) - part1.Length) : "")
                     .Select(x => int.TryParse(x, out var number) ? number : 0).Where(x => x > 0).OrderBy(x => x)
                     .TakeWhile((x, i) => x == i + 1).LastOrDefault() + 1;
 
             return $"{part1}{nextNumber}{part2}";
         }
     }
-}
\ No newline at end of file
+}