The work aims to study the microstructure evolution of high emissivity borosilicate coating on large area reusable rigid insulation tile in the ascent temperature environment. Thermal exposure was carried out to simulate the temperature condition of reentry at 1250 ℃ and 1300 ℃, so as to investigate the evolution rules of coating microstructure at high temperature. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD were respectively used to characterize the microstructure and the phase of coating before and after thermal exposure. The coating surface generated micropores after thermal exposure at 1250 ℃ and 1300 ℃, especially in the zone of radiation agent particle (MoSi2 and SiB4) aggregation. The number of micropores increased with the number of thermal exposure. In addition, intermediate transition layer was re-sintered and stratified after 5 times of thermal exposure at 1300 ℃. The side near surface gradually became dense and was sintered together with the surface, while the other side was sintered with the substrate. Cristobalite phase precipitated on the coating after thermal exposure and the amount of crystallization was positively correlated with the number of thermal exposures. The intermediate transition layer is gradually destroyed and the structure of coating is also transformed from a two-layer to a single-layer after thermal exposure at 1300 ℃. The capability of thermal shock resistance decreases and the coating is easy to cause crack, peeling, etc. The cristobalite precipitated on the coating after thermal exposure will affect the size and stability of coating. The thermal exposure can cause oxidation of the radiation component and form micropores, which reduce the compactness of surface coating and lead to the peeling of coating.