The surface temperature of Stirling cryocooler has a direct effect on the performance of infrared detector, so the optimization of the cooling design of Stirling cryocooler is particularly important in the thermal vacuum environment. In order to optimize the heat dissipation conditions of Stirling cryocooler applied in thermal vacuum environment, the thermal simulation analysis of the thermal vacuum environment of Stirling cryocooler based on the Ansys calculation platform is carried out, and the water-cooled heat dissipation fixture of Stirling cryocooler is designed. The simulation calculation and experimental research are carried out as well. The results show that the driving plate is the highest temperature position in the cryocooler. A water-cooled heat dissipation fixture with groove structure made of copper is designed, which can effectively reduce the surface temperature of Stirling cryocooler. Under the condition of constant external environmental temperature, the temperatures of Stirling cryocooler motor shell and the water-cooled heat dissipation fixture increase when the inlet temperature increases. Moreover, the temperature differences between inlet and outlet of the water-cooled heat dissipation fixture gradually decrease.