A modulated spraying nozzle control system can be used for variable rate chemical application. The transient numerical simulation of high speed valve was modeled by CFD software Fluent to research the flowing character in the solenoid valve. The result showed that there was suction pressure generated at outlet of valve when it just opened, which would result in air-sucking and effect atomization quality, also at lapse in the shut down time of the valve, it was harmful for the atomization. When the valve was opening, the pressure of outlet was equal to that of inlet, when it was just opening, both the pressure and flow rate met the maximal level, with two zones increased sharply. The forming, developing and transporting complex process of vortex was found during the valve opening and closing.