The liquid level control system based on the SIEMENS PLC S7-200 is introduced in this paper. The interface of man-machine conversation is designed with Configuration software in order to monitor the operation status of the liquid level PLC control system. 介绍了利用西门子S7-200可编程控制器实现液位PID控制系统,并利用组态王软件制作人机对话界面,监控液位PLC控制系统的运行情况。