Abstract: The heat exposure test at 650℃ for different times was carried out on FGH97 powder metallurgy superalloy. The evolution rule of microstructure was analyzed by scanning electron microscopy, and the γ' phase in the course of evolution was quantitatively characterized. The results show that with the extension of heat exposure time, the shape of γ' phase in the FGH97 powder metallurgy superalloy changed from regular square and triangle to butterfly or octagon, and then to irregular shape such as strip and rod. The cracking occurred in the secondary γ' phase and the amount of tertiary γ'phase particles in the grains decreased. As the heat exposure time increased, the average equivalent diameter of γ' phase in the FGH97 powder metallurgy superalloy first increased and then decreased, the shape factor decreased, the volume fraction increased, and the amount of γ' phase gathered at the grain boundaries increased significantly.