The stable operation of the sealing assembly plays a vital role in the performance of the hydraulic viscous clutch. In order to research the leakage characteristics of the clearance seal of the hydraulic viscous clutch, a clearance seal model is established based on the computational fluid dynamics. The validity of the model is proved by comparing the leakage of the experience in a self-build sealed test-bench, and the effects of seal clearance and oil temperature on the flow velocity, leakage and friction torque are analyzed by numerically simulating. The calculation results show that the decrease of clearance leads to the decrease of outlet area and leakage. Although the variation of rotational speed has little effect on leakage, it can effectively alter the friction torque especially in the case of small seal clearance. By comparing the leakage of each outlet at different temperatures, it is found that the leakage increases drastically when the oil temperature is larger than 70℃.