Abstract: The comprehensive detector of the photoelectric system outside the box is an important accessory of the high and low temperature performance test device of the photoelectric imaging system, and the multispectral optical window is an interface between the high and low temperature box and the external target simulator. According to the application requirements and material analysis results, the multispectral ZnS was selected as the optical window material. Through the heat conduction theory, the low-temperature service state of the optical window assembly was analyzed, focusing on the influence of the window assembly heating under the low-temperature condition on the surface shape of the window assembly, and the structural form to realize the micro-stress assembly and the design scheme to solve the frost and fog of the window assembly under the low-temperature condition were put forward. According to the extraction, processing and data fitting of finite element calculation results by sigfit and the analysis of caliber by CODE V, the root-mean-square (RMS) value of wave aberration of Φ 310 mm window assembly in the temperature range is better than λ/15. The above contents all meet the optical performance requirements of window assembly. And finally, it was verified through the physical prototype. The experimental results show that the structural design scheme of multispectral optical window assembly not only meets the requirements of multi band usage, but also meets the requirements of low-temperature defrosting and defogging, and ensures the optical performance requirements under high and low temperature conditions.