The phase of the occurrence of the viscous torque is determined by the division of the wet clutch engagement process.They are pure oil film shear stage and mixed friction stage.By considering the effect of the pressure and centrifugal force，radial velocity and flow were calculated.According to the modified Reynolds equation and Newton’s law friction,the model of oil film thickness variation and the viscous torque were established,and it was simulated by Simulinkl.The coefficient equation was introduced to modify the theoretical formula,and the coefficient of independent variable in the coefficient equation was determined by testing the actual torque with many experiments.The result of comparison between the test curve and the calculated curve of the viscous torque shows that the calculation formula of viscous torque can reflect the experimental situation better.The calculation results show that the centrifugal force and the pressure difference have great impact to the viscous torque.Due to the compressibility of the fluid flow,the hydraulic control effect is reduced,the influence of centrifugal force caused by the speed of the viscous torque is enhanced,so the influence of rotational speed on the viscous torque is larger than that of control pressure.