This paper studies FGH96 P/M Superalloy dynamic recrystallization phenomenon under isothermal forging conditions. Curves of work hardening rate θ versus flow stress σ and RTT curve of dynamic recrystallization are gained through the analysis. At the same time, some parameters are confirmed including peak strain, critical strain and the maximal softening strain. On the basis of the analysis, the type of FGH96 P/M Superalloy dynamic recrystallization is exactly estimated. The quantitative metallography method is adopted to determine the recrystallized grain size. With combining the obtained data and parameters, FGH96 P/M Superalloy dynamic recrystallization mathematic model is established by regression method. At the same time, the forging process of FGH96 P/M superalloy is simulated by using software MSC/Superform under different deformation conditions such as deformation temperature and deformation velocity. The contour images of the grain size distribution under different conditions and different deformation degree are gained and analyzed. With the analysis, it is known that the effect of the different deformation conditions on the microstructure of the forging is obvious and there is different distribution of the grain size on various locations, which indicates that the deformation degree of the billet also has influence on the grain size.