Abstract: The traditional middle small sized machinery liquid pressure servo system of turbine governor has some defects, such as: more machinery members, complex oil channels and pipelines, expensive cost and high failure rates. Aiming at these defects, the new system uses screw members in stead of the traditional member system and employs controlled sliding valve in stead of main pressure distribution valve, and, in result, the system structure is simplified and more reasonable. The data of main parameters are as follows:① rotational speed dead zone ix≤0.08%;② linear error of static characteristic curve ε＜5%；③ degree of un accuracy of servo system ia ＜1.5%；④ no movement time of the servomotor Tq＜0.2s；⑤ relative speed oscillating value Δx≤0.25% under autounload operation in 3 min ；⑥ in transition process of throwing off load 100%,wave number N＜2，regulating time T＜40 s; The improved system possesses the advantages of simple operation,convenient maintenance and service long operating life and high reliability