Abstract: The thermal deformation of a radiometric calibration optical-structure system under simulated space environments would cause a great damage to the imaging quality of the system, and reduce the precision of the calibration test eventually. In this paper, a finite element model of such a system is built. Based on the model, with the temperature values at nodes obtained in the radiometric calibration test for the satellite multi-spectral scanner, the distribution of the thermal-structure coupling deformation is calculated and analyzed. The results show that the thermal distortion of the optical bracket would cause rigid displacements of the primary mirror and the primary reflector, making them off the axis or acclivitous and the black body off the focus, and changing the focal distance of the system in a non-uniform steady-state low temperature condition. But the root-mean-square (RMS) values of deformation of the anamorphic mirrors are both less than one fortieth of the wave length, within the actual surface shape accuracy requirements of the optical system.