When accident overload occurs, there are many differences between security and stability control equipment and relay protective equipment. This paper points out the differences in criterion and action of overload, which are used in security and stability control equipment and relay protective equipment. First, it points out that the line or transformer’s backup protection should act rightly when accident overload occurs. Second, it introduces specific ideas in system and design to prevent false judgment. And third, it introduces some methods which can prevent over excess control measures. The practical operation experience proves that these methods can improve the operation reliability. So, the methods are right and effective.