In order to solve the problem of constant-pressure water supply in high rise residential buildings, to fulfill the low power, low-cost demand, here I propose LOGO! And a water supply equipment controlled by frequency converter. By collecting field measurement signals through the pressure sensor together with LOGO! Logic control signals, this equipment can change the frequency and voltage of the inverter, control the pump's rotation rate and finally, meet the constant-pressure water supply demand. This paper also describes the hardware circuit and the software design of LOGO! in detail. Practice has proved that: The frequency converter and the LOGO! control are highly reliable, easily operated and conveniently maintained. Therefore the object of energy saving can be achieved successfully.