The hot compression experiments of forged IN718 nickel alloy under different process parameters were carried out, and the microstructures of IN718 alloy under different thermal deformation conditions were analyzed by OM, SEM and TEM. The results show that the rheological stress of IN718 alloy increases with the increasing of strain, which is a typical plastic rheological process with dynamic recrystallization. Under various thermal deformation conditions, the alloy shows a significant peak phenomenon, and the peak stress of alloy decreases when the temperature increases or the strain rate decreases. Furthermore, the alloy grows into many tiny recrystallization grains at 1050 ℃, and its average grain size gets larger after the heat treatment temperature rises. As the strain rate increases, the grain size decreases continuously. Under 1080 ℃ and strain rate of 0.001 s-1, the plastic deformation of sample occurs, and the small γ′ phase in the grain has obvious inhibitory effect for the dislocation movement.