After grain refinement through hot-forging and δ-phase precipitation and recrystallization heat-treatment processes, the high temperature tensile experiments were carried out to investigate the effect of heat treatment and deformation process on the superplasticity of Inconel 718 alloy. Two tensile processes were used as follows: the maximum m value superplastic deformation method and the strain-reduced superplasticity deformation process based maximum m value method. The results indicate the fine and homogeneous grain structure of Inconel alloy is obtained by hot forging, δ phase precipitation and recrystallization heat treatment processes, and the δ phase can play a role in controlling grain size during recrystallization annealing and hot deformation. Upon stretching by the above two processes at 950 oC, the percentage elongations of Inconel 718 alloy are improved from 340% and 566%, respectively. The results show that the higher value of percentage elongation can be obtained by the strain-induced superplastic deformation process based maximum m value method