Based on the superelastic properties exhibited by shape memory alloy, a cosine type constitutive model and a solid isotropic material penalty model were combined to describe the characteristics of shape memory alloy. A material interpolation function was established and a variable density topology optimization method was used to achieve structural topology optimization design considering the nonlinearity of shape memory alloy. The proposed method was applied to design the typical two-dimensional and three-dimensional structures. Static analysis and martensitic transformation evolution analysis were used to analysis the structure obtained by the proposed optimization method. The results show that the structure optimized by the proposed method has better mechanical properties compared to the traditional one. In static analysis, the maximum internal stress decreases by 19.57% and the maximum displacement decreases by 31.03%. In the analysis of martensitic transformation evolution, the maximum volume fraction of martensite at the end of loading decreases by 20.27%. The proposed optimization design method results in the even overall stress distribution within the structure, less prone to local stress concentration, and less deformation caused by martensitic transformation.