With the introduction of high by-pass turbofan engines into both commercial and military aircraft industries, the fabrication of large size fan blade through superplastic forming/diffusion bonding (SPF/DB) has become a pivotal technique of turbine fan engine. There are three key steps to form a hollow blade: twisting, hot forming and SPF. In this study, a three dimensional finite element method (FEM) model is established to simulate the forming process of titanium fan blade, in which the mechanical behavior of TC4 obeys Backofen’s equation. Based on the numerical modeling, the influences of key factors such as the twisting rate, descending velocity, frictional coefficient, strain rate, the sheet thickness ratio of core sheet to face sheet on the forming force were studied. The results show that with increasing of the twisting rate, descending velocity, strain rate, the sheet thickness ratio of core sheet to face sheet, the forming forces increase; however the frictional coefficient has little influence on the forming force