In the degreasing process of automobile coating, the temperature of the degreasing liquid is an important parameter that affects the degreasing effect. According to the degreasing process and control requirements of an automobile factory, an automatic control system for the degreasing process was designed based on S7-300 PLC. Aiming at the temperature of the pool liquid, a temperature-flow cascade control program was designed, The man-machine interface is designed using WinCC configuration software. Good control results have been achieved in practical production applications.