FY-4 is the satellite on geostationary three-axis stable satellite platform. Due to the influence of severe external heat flux on the daily cycle and annual cycle, temperature of the scanning fame and telescope of the imager on board will be fluctuated above 40℃. How to adapt the optical machine structure to the severe environment temperature change and ensure the good image quality are the international problem. Matching design with various material and using proper structure is avoiding and reducing distortion of structure and debasing of image. The data on board indicating, the imager has overcame adverse effect for severe fluctuate when day and night. When star sensing, each diffuse spot almost covers only one pixel, and there is not much difference between midday and midnight.