Based on the process conditions and control requirements of the constant pressure water supply system, the automatic control system of the constant pressure water supply was developed. The control circuit of variable frequency one for two was designed, and the constant pressure value PID control program, the water pump non-disturbance switching control program and the limit value and interlock protection program were compiled. The experimental system has simple structure, easy to use and strong portability. It is suitable for teaching and experimental training in the course of electrical and automation engineering in and out of class of universities, and has achieved good results in practical teaching and application.