For the inertial friction welding (IFW) of GH4169 superalloy, a finite element (FE) simulation model was established to investigate the transition of interfacial friction regime and transient evolution law of thermal processes variables such as heat generation and temperature. The accuracy of the FE model is verified by the experimental data. The results show that the Coulomb friction zone occupies the whole interface at the beginning of the welding process, and gradually shrinks from 0.54 s and disappears completely at 9.60 s, while the shear friction zone builds up at 0.31R0 (R0 is the radius of the workpiece) and expands to the entire interface. Based on the simulation results, an analytical equation describing the evolution of the Coulomb friction zone is proposed. The coupling relationship and variations of heat flux, frictional stress and temperature at the interface caused by the transition of friction regime are analyzed. The results show that the transition of interfacial friction regime from the Coulomb friction regime to the shear friction regime is beneficial for temperature homogenization at the interface.