Hydrodynamic retarder under different vane degree condition was simulated. By using the time averaged N-S equation and the standard k-εturbulence and the SIMPLEC algorithm simultaneously, the internal characteristics of flow field were simulated. The calculated velocity, pressure and turbulent kinetic energy distribution of the turbulent flow in hydrodynamic retarder were given. The method of loss analysis was proposed which changed value of Rothalpy was used to compare the retarder ability. The result shows that the model under 55° vane degree has the biggest impact because the loss of friction and impact made hydrodynamic loss most.