Abstract: The heat transfer performance of a heat sink directly affects the simulation results for the space cold environment. This paper establishes a heat sink geometry model, to simulate the heat transfer performance of the heat sink based on the hydrodynamic theory and the finite element method. In the pressure-velocity coupling computation, the Simple algorithm is used and the RNG turbulence model is employed to calculate the heat sink temperature distribution and the heat transfer parameters. The influencing factors of the heat sink temperature uniformity and the heat transfer characteristics are analyzed. The results show that the heat sink temperature uniformity is poor when the flow rate is small. Only above a certain flow rate can the heat sink temperature distribution uniformity be ensured. The increase of the flow rate can improve the heat transfer efficiency of the heat sink, but it also increases the fluid pressure loss. The heat transfer and resistance should be taken into account to determine the optimal inlet flow rate. The forms of the inlet and the outlet do not affect the heat sink wall temperature uniformity when the effective size of the heat sink is small.