Abstract:The method of UDF in Fluent software was used for the dynamic simulation of seal clearance servo hydraulic cylinder. The relationship between temperature, pressure and the hydraulic oil viscosity was defined through programming, and the influence of piston periodic motion, temperature as well as pressure on interstitial fluid flow of the hydraulic cylinder clearance was analyzed. The results show that: the oil viscosity changes with the average temperature of fluid increased gradually. The rising in temperature, the decrease is in hydraulic oil viscosity, the fluid resistance and hydraulic pressure reduced as well, on contrary, the hydraulic pressure is increased. Viscosity decreases continuously, leakage flow rate will continue to rise, but the increasing of leakage speed will be slow down gradually, finally reached a steady state. When the viscosity changes, the interstitial fluid field inner wall friction is increased gradually along with time. When the hydraulic cylinder running up to a certain time, inner wall friction will tend to be stable state.