Aiming at the problems of large number of clapboards and difficult assembly process in the traditional design scheme of infrared detector cold shield, a simplified design method of infrared detector cold shield is proposed in this paper. This method reduces the number of cold shield partitions, the thermal mass of cold head and the limitation of space on cold shield design.Because this method ignores the window seat of thermal radiation, two kinds of cold shield structures of a mid-wave infrared detector are designed by using the traditional scheme and the simplified scheme respectively, and the LightTools software is used to simulate the influence of window seat thermal radiation on infrared detector and the suppression efficiency of cold shield to field light in order to validate its feasibility. The simulation results show that when the ambient temperature of the detector is 344 K, the noise difference caused by the thermal radiation of the window seat on the infrared detector is not more than 0.3 mV.The difference is negligible compared with the signal intensity, and the suppression efficiency of the two cold shields is only 0.2% different, which verifies the feasibility of the design method.