Abstract: Taking Lanzhou Cigarette Factory as an example,the practical application of automatic constant pressure water supply system in cigarette factories was introduced.The close-loop control of water pressure in this system was realized by optimizing the number of working pumps and the rotation speed of variable pump motor.The speed of motor was regulated by a frequency converter to stabilize water pressure and save energy when the flow rate in pipeline fluctuated.PLC Controller was adopted to realize the logical control of pump group and valves and monitoring real time running parameters and control points.The system connected to a computer at higher level in power management system by a standard communication interface to optimize the control of water supply.The practical running results showed that energy consumption decreased by 27.1% to 48.8% with the working frequency of pump motor of 40-45 Hz.The resistance and restriction loss in pipeline and the labor intensity of operators were reduced,and the working lives of water pump and motor were prolonged.