Superplastic forming( SPF) process for TC4 large hemisphere shell of variable thickness had been researched in this article. With the help of numerical simulation method,the characteristics of thickness distribution after direct SPF and direct-reverse SPF process were analysed,and the advantages of thickness distribution after directreverse SPF were pointed out. The key parameters of surface curve optimization of the reverse SPF die and its influence on the thickness distribution were given. According to the optimized simulation data,the experimental parameters were designed and verified on the basis of theoretical analysis. The results show that the actual thickness distribution of the part can be well predicted by the numerical simulation. The thickness of the part is redistributed according to need by using optimized SPF forming die. The tensile and yield strength of the material decreases slightly and the elongation increases after SPF. The direct-reverse SPF process can improve material utilizing rate and efficiency of subsequent turning operation obviously,reducing total manufacturing costs.