Abstract: Based on the study of high quality turbo disk and compressor disk of aero engine,the inertial friction welding process of IN-718 is analyzed and simulated with finite element numerical simulation method(FEM),and based on the physical theory of metal plastic deformation,a model of microstructure evolution of inertial friction welding process of IN-718 is developed.Meanwhile,with the theory of recrystallization of superalloy in thermal deformation process and the corresponding relationships among recrystallization volume,grain size and thermodynamics parameters(strain rate,strain,forming temperature),the numerical simulation of the recrystallization microstructure of the heat affected zone in inertial friction welding is carried out,therefore,a sound reference is provided for the optimum choice of the welding thermodynamics criteria,as well as for the improvement of the welding performance of IN-718.