In order to simulate the grain evolution of superalloy at different heat treatment temperatures, the phase field model was improved by introduced the Arrhenius relationship, in order to describe the quantitative relationship between the grain boundary movement and temperature. Based on the improved phase field model and fitted model parameters, the grain average size and morphology evolution of superalloy FGH96 during the longer heat treatment process were simulated, and the simulated results were compared with the experimental results. The results show, the calculated data coincide with the experiment data, the evolution law of grain is consistent with the experimental observation and theoretical analysis. These results prove that the grain boundary mobility M in the Arrhenius relationship is suitable for simulating the heat treatment process at the corresponding temperature. At the same time, the feasibility of the improved method and accuracy of the fitted parameters of the phase-field model are verified.