Abstract: To investigate the effect of strain rate on the microstructural homogeneity of hot extruded FGH96 powder metallurgy superalloy after supersolution treatment, thermal compression tests and double-cone isothermal compression experiments were conducted, combined with finite element simulations of isothermal compression experiments, the evolution characteristics of grain structures of the alloy in supersolution treated state under different strain rates were comparatively analyzed. The results show that the thermally compressed specimens deformed at 1070 ℃ and subsequently subjected to supersolution treatment at 1150 ℃ exhibit a mixed coarse-fine grain structure, and the microstructural heterogeneity increases significantly with the increase of the strain rate. At high strain rates, the proportions of both fine grains(<5 μm) and coarse grains(>45 μm) increase simultaneously, leading to intensified grain size differentiation, whereas a relatively uniform grain size distribution is obtained at low strain rates. For the double-cone specimens, pronounced abnormal grain growth is observed in the variable cross-section apex region, particularly under the low compression rate of 0.1 mm/s, the maximum grain size reaches 587 μm. Finite element simulations reveal that this abnormal grain growth is not primarily induced by temperature rise, but is attributed to the sharp increase in strain rate at the apex region during the later stage of compression. The localized concentration of deformation energy subsequently promotes heterogeneous grain growth during the supersolution treatment. These findings demonstrate that the strain rate is a critical process parameter for controlling the microstructural homogeneity of FGH96 powder metallurgy superalloy after supersolution treatment, providing direct guidance for the optimization of isothermal forging process.