Abstract: The on-off behavior characteristics, spool displacement static characteristics and micro-amplitude oscillation characteristics of PWM high speed on-off valves have been studied through an approach of combined digital simulation and testing. The regular patterns of the on-off process for the spool are analyzed and the on-off behavior characteristic mathematic models built up. The static, characteristics of spool traverse are completely and systematically studies, and the factors fc, t1, t2, t3, t4, that affect the static characteristics and thereby the performance of the whole on-off valve control system are discussed in detail. Mechanism for the formation of micro-amplitude oscillation waves accompanying the output wave of PWM high speed on-off valve control system is analyzed.