Abstract: The density, sound velocity and modulus of FGH97 PM superalloys were measured and calculated, which had passed through high temperature tests and high temperature stress endurance tests after various time. Meanwhile, the microstructure was also analyzed. The influence of long-term high temperature and stress on the density, sound velocity and modulus of FGH97 PM superalloys were researched. The results show that:under conditions of high temperature and high temperature stress, the density, sound velocity and elastic modulus of FGH97 PM superalloys decreased gradually with the increase of time; each characteristic parameter had a more outstanding change under high temperature stress endurance tests than high temperature tests; the time variation of microstructure were that the carbide coarsened, the morphology, volume fraction and size of γ' phase changed, and the thermally induced porosity, creep cavity and microcracks appeared in the grains or on the grain boundaries.