With the increase of population density and the improvement of human economic level, the emergence of high-rise buildings has put forward higher requirements on infrastructure such as building hydropower, traditional water supply methods have disadvantages such as secondary pollution, unstable water pressure, and high energy consumption. Therefore, variable frequency and constant pressure water supply have gradually become the main method of water supply for high-rise buildings. In order to meet the higher water supply requirements of urban residential quarters, a PLC-based variable frequency speed regulation and constant pressure water supply monitoring system is designed. The main control objective is to stabilize the water supply pressure. The inverter is driven by a three-step variable frequency control method. The pressure sensor of the water supply pipeline detects the pressure value in real time, uses the PID control algorithm, and outputs the frequency setting value to the inverter through the PLC, and then realizes the control of the water pump outlet pressure and achieves the purpose of constant pressure water supply. On the basis of considering the program capacity and expansion requirements, this system selects S7-1200 compact PLC as the main controller, uses modular programming as the basic concept to control the PID control program, logic switching program, and alarm breaking the program has been programmed and debugged. The test result shows that the designed control algorithm is effective, the logic function is complete, and it has a certain application and reference value. The frequency conversion constant pressure water supply system can realize the automatic switching of the operation status and the number of pumps in operation under different water supply requirements, and further improve the automation degree of the system on the basis of meeting the control requirements.