Abstract:This paper mainly introduces the design and performance of SoftPLC Ladder Diagram editing software. Adoppting Qt as the developing tool which applied in multi-operating system, so the system is more opening. Based on in-depth analysis of the ladder diagram's overall structure, the systerm's class hierarchy is designed using object-oriented method, which enhances the efficiency of the software. Applying the storage structure of double layer and double linked list makes the dynamic editing operations more flexible and convenient. The source language converted to instruction list through sequential scanning the ladder diagram makes the process simpler. At last, the experimental results in testing the software show that the design method is accurate and feasible.