Plus Width Modulation (PWM) is widely used in proportional control systems for its characteristics of efficient, flexible and strong ability of anti-interference. Due to the friction and hysteresis of electromagnet, hysteresis phenomenon was caused to exist in characteristics of hydraulic valve in steady-state, and the dynamic response performance of the valve was seriously influenced by the hysteresis. The relatively effective method of reducing the hysteresis was by superimposing dithers with certain frequency and amplitude to the diving signal, currently, changing the duty ratio of PWM was widely used to implement the superimpose dither to the signal. Through both the theoretical deducing and experimental study, it proves that dither with independent adjustable frequency and amplitude can be generated by changing the frequency of the PWM, in this way of superimposing dithers, the average current of electromagnet and dither current can be controlled independently by the duty ratio and frequency of PWM separately.