The constant speed downhill control of the vehicle with a hydraulic retarder is a process of timevarying, nonlinearity.In order to make the vehicle constant speed downhill control meet the requirement of no static difference and quick response,by analysing the characteristic of control of hydraulic retarder and fuzzy control, a strategy based on fuzzy control with hierarchical variable universe was proposed to realize vehicle constant speed downhill control. The dynamics model for heavy truck downhill and variable universe fuzzy controller were established by MATLAB/Simulink, and simulation analysis for control strategy was conducted. The control effects of vehicle constant speed downhill control were studied and compared with traditional fuzzy control. The results show that the control strategy proposed can effectively realize the performance requirements of constant speed downhill control, and the control effect is obviously superior to traditional fuzzy control.