The variable-frequency constant-pressure water supply system takes the water pressure in the pipe network (or the water flow of users) as the set parameter, and automatically adjusts the rotating speed of the pump motor by controlling the output frequency of the frequency converter through a microcomputer, so as to realize the closed-loop adjustment (PID) of the water pressure in the pipe network, and make the water supply system automatically and constantly stabilize at the set pressure value: that is, when the water consumption increases, the frequency increases, the rotating speed of the pump accelerates, and the water supply increases accordingly; When the water consumption decreases, the frequency decreases, the pump speed slows down, and the water supply decreases accordingly, thus ensuring the water supply efficiency and achieving the purpose of improving the quality and efficiency of water supply, "how much water is used, how much water is supplied"; Using this equipment, there is no need to build a high-level water tank or water tower, and there is no secondary pollution to the water quality. It is an ideal water supply equipment for modern buildings.