diff --git a/Providers/FreeSql.Provider.Dameng/DamengUtils.cs b/Providers/FreeSql.Provider.Dameng/DamengUtils.cs
index 930bb5c1..7376f7c4 100644
--- a/Providers/FreeSql.Provider.Dameng/DamengUtils.cs
+++ b/Providers/FreeSql.Provider.Dameng/DamengUtils.cs
@@ -23,14 +23,21 @@ namespace FreeSql.Dameng
             {
                 case DmDbType.Bit:
                     if (value == null) value = null;
-                    else value = (bool) value == true ? 1 : 0;
+                    else value = (bool)value == true ? 1 : 0;
                     dbtype = DmDbType.Int32;
                     break;
-               
+
                 case DmDbType.Char:
                 case DmDbType.VarChar:
                 case DmDbType.Text:
-                    value = string.Concat(value);
+                    if (value == null)
+                    {
+                        value = (string)null;
+                    }
+                    else
+                    {
+                        value = string.Concat(value);
+                    }
                     break;
             }
             var ret = new DmParameter { ParameterName = QuoteParamterName(parameterName), DmSqlType = dbtype, Value = value };
@@ -56,8 +63,14 @@ namespace FreeSql.Dameng
                         case DmDbType.Char:
                         case DmDbType.VarChar:
                         case DmDbType.Text:
-                            if(value != null)
+                            if (value == null)
+                            {
+                                value = (string)null;
+                            }
+                            else
+                            {
                                 value = string.Concat(value);
+                            }
                             break;
                     }
                 }