In order to improve the dynamic response and characteristics of the highspeed onoff valve, structure parameters optimization was carried out in three different aspects: enlarging the pilot area of servo spiral mechanism, reducing the moment of inertia of the electro mechanical converter and using the variable ratio for the transmission device to increase the input torque of valve. Based on the analysis of the work principle in servo spiral mechanism, the new type of spool with slope groove was proposed. The bigger pilot area gradient and better response can be gotten while spool rotates were compared with round pilot hole in spool. The six pieces of structure with 26° angle, which located evenly in axial direction, were designed to lower the moment of inertia compared with the original three pieces with 52°. The variable ratio in transmission device was presented, which made the spool have more moment to reduce the chance of valve stucking at the beginning of valve opening. Curve of ration and moment with variable ratio were given to prove it. After that, mathematical model of the system was built to describe the working process. And the simulation was done in Matlab to get the logarithm amplitude versus frequency characteristic curve. The frequency was 240Hz while the logarithm amplitude was -3dB in curve and the better dynamic performance can be gotten with bigger pilot area gradient in spool. Finally, the experimental device was built to validate the theory analysis. The step response time with full scale was 8ms under 21MPa，and the leakage rate was 5.6L/min. The valve with the new structure worked better compared with 18ms under 28MPa in original valve.