Under the premise of satisfying the function of the water valve, the solenoid coil of the onoff valve is optimally designed to minimize the number of turns, and the electromagnetic force of the electromagnetic coil can meet the requirements. The suction coil model and temperature rise model of the water valve were established. The water valve onoff switch of the electromagnetic coil, according to the analysis results, the valve structure and the coil turns were optimally designed to determine the number of turns of the coil. In order to be able to see the image of electromagnetic coil electromagnetic field changes after the improvement, ANSOFT Maxwell analysis software simulation analysis of electromagnetic onoff switch of electromagnetic field was carried out by electromagnetic field. The results show that the improved not only can save the copper wire, but also the water valve, electromagnetic suction, temperature rise and other switch electromagnetic valve parameters can meet the job requirements.