As an important part of infrared detector assembly, split Stirling refrigerator has great influence on the performance of infrared detector assembly in practical application. Among them, the coupling gap between dewar and Stirling refrigerator is one of the most important factors affecting the performance of infrared detector. Therefore, the effect of the coupling gap on the performance of infrared detector is studied experimentally in this paper. When the chip temperature is 75 K and the cold head temperature of the refrigerator is 70 K, the deformation of the cold finger and dewar is simulated, and the coupling gap deformation is 0. 0096 mm.The low temperature environment has little influence on the deformation of the cold finger and dewar of the refrigerator, and the influence of the deformation of the cold finger and dewar on the coupling gap can be ignored. The experimental results show that the cooling time of the infrared detector module increases with the increase of the coupling gap. With the gradual increase of time, the corresponding DC currents of different coupling gaps are also different. At the same time, the smaller the coupling gap is, the smaller the DC current is. The diode voltage gradually increases and becomes stable with the increase of time. Before reaching the temperature control state, the smaller the coupling gap is at the same time, the larger the diode voltage is.