Millimeter-wave and sub-millimeter-wave detectors, when operating in geostationary orbit, are influenced by environmental thermal radiation in the performance of their subsystems. Based on in-orbit temperature field data, finite element analysis is employed to simulate the thermal deformation of the quasi-optical feed network; the GRASP software is adopted to fit the positional and surface parameters after the device's thermal deformation, and to simulate the changes in electrical performance when the quasi-optical feed network is subjected to on-orbit environmental thermal radiation. The results show that environmental thermal radiation has a certain impact on the electrical performance of the quasi-optical feed network, and by adopting temperature control measures, it is possible to avoid performance changes caused by temperature variations in orbit.