Abstract: The structure of the spacecraft in orbit is vulnerable to the external heat flow environment, with a huge temperature gradient and related with structural thermal deformation. In order to improve the effectiveness of related ground assessment test, a high realistic simulation of the on-orbit heat flow is required, and high-precision thermal deformation measurements are to be performed to obtain the structural deformation data. This paper presents a method for the thermal deformation test, that is, the external heat flow simulation using the solar simulator, combined with the non-contact photogrammetry of an antenna in a vacuum cryogenic environment. The on-orbit temperature distributions of the antenna are simulated, and a large amount of the point cloud deformation data on the antenna are accurately obtained. The comparisons show that the measured data of the antenna’s deformation are consistent with the simulation analysis, and the deformation measurement accuracy is better than 15 μm over the entire 1.5 m aperture. Thus the effectiveness of the solar thermal deformation test method is verified, which can provide a new test approach for the on-orbit thermal effect simulation, test and evaluation for the spacecraft structure.