In order to find a method to reduce excessive sheet thinning in the forming process of small half-apex angle parts by incremental sheet forming, a finite element model (FEM) for simulating double-stage process is developed in ABAQUS. Then, the simulation results, such as sheet thickness distribution and equivalent plastic strain history, are compared with those of single-stage simulation. The effects of double-stage on formability of sheet are discussed. The results show that using double-stage process instead of single-stage in forming parts, the maximum deformation is nearer to the parts’ bottom surface, and the maximum equivalent plastic strain of node A, B, C is reduced by 66.2%, 81.9% and 36.0% respectively. The sheet thickness is better distributed, and the minimum thickness increases by 16%. In addition, double-stage incremental forming can greatly improve the formability of sheet. The simulation results are in a good agreement with experimental results.