With the development of remote sensing satellites and space optics, the resolution of spaceborne remote sensors is becoming higher and higher and the diameter of main reflectors is becoming larger and larger. The structure type, weight, support installation and temperature environment of the space reflector will directly affect the performance of the whole optical system. In this paper, the design of supporting structures is discussed. The solutions to the deformation caused by mirror gravity and to the stress and deformation resulting from the different thermal expansion coefficients of the mirror and the support structure are emphasized, so as to ensure the cooling and temperature uniformity of the reflector and enable the image quality of the optical system to meet the design and application requirements.