Title: Design of Traffic Lights Control System Based on S7-200 PLC ABSTRACT Because of the characteristics with high dependability, modularization structure and easy programming, PLC is used to do real-time gathering, controlling and communicating with transducer. In the design of traffic lights control system, PLC is used to control equipments such as traffic lights,and realizing the communication with monitoring software of host computer. We choose the KingView software as the monitoring software, which is from Beijing Wellin control Technology Development Co. Ltd. This thesis consists of seven chapters. Firstly, the paper clarifies the meaning of subjects and main contents of research. In the second chapter, we introduce the structure and work principle of PLC and introduce the SIEMENS S7-200 PLC and its characteristics particularly. Chapter three emphasizes the configuration software. And then we emphasize the KingView software. Chapter four designs the structure and the configuration of hardware and software for traffic lights control system. In the fifth chapter, we introduce the configuration of monitoring software of this system. In the sixth chapter, we introduce the debugging of the system. The last chapter is the conclusion of the whole research.