Aiming at the problems of inconvenient remote operation of a petroleum steel pipe factory and unstable cooling water pressure, insufficient or short-term water shortage in the water supply system, this paper designs a variable frequency constant pressure system using industrial computer + Siemens S 7-300PLC $+\mathbf{P}$ ROFIBUS bus technology Water supply control system. The system selects the continuous PID controller FB41 function block in Siemens industrial communication programming software STEP7 V5.6 to control the operating frequency of the frequency converter, so as to realize variable frequency and constant pressure water supply. The upper monitor realizes the real-time monitoring of on-site working conditions, alarm screen display, historical data storage, printing and other functions through the configuration software WinCC6.4, and uses industrial Ethernet to communicate with the industrial computer. The system satisfies the production requirements, facilitates remote monitoring, and improves the work efficiency of operators and the automation level of enterprises.