In spacecraft thermal control technology, infrared heating cages are used to simulate the external heat flow reaching each surface; however, the rationality and accuracy of this method must be re-evaluated when the feature size of the simulated surface decreases progressively. In this study, simulation analysis and design optimization of infrared heating cages were conducted based on a micro-space camera with the most sensitive heat dissipation surface for external heat flow. The finite element method was used to establish a simulation model of the infrared heating cage black-sheet heat flow meter system, and the influence of the traditional infrared heating cage control method on the total arrival energy and heat flow density uniformity of the simulated surface was analyzed. The results show that the heat flow density uniformity of the simulated surface was improved by appropriately enlarging the heating cage and adjusting the position of the heat flow meter paste to ensure that the total arrival energy satisfied the conservative design principle.The statistical variances in the heat flow density of the radiator surface before and after the optimized design were 102.0 and 27.0, respectively, and the homogenization effect was significant. This study can be used as a reference for the accurate simulation of heat flows on other tiny space surfaces.