Superplastic forming has emerged as an important manufacturing process, large deformation always occurs during superplastic forming, time-consuming remeshing is necessary while the finite element method (FEM) is used to analyze metal forming process. Meshless methods with no meshes can avoid this problem and overcome those problems in FEM. In this paper a meshless method based on the reproducing kernel particle method (RKPM) is applied to analyze Magnesium Alloy (MB15) thin sheet superplastic tension forming. A superplastic meshless method modeling program is set up, and background cells are used to compute the integrations in weak form equations and the mixed transformation method (MTM) is used to impose the essential boundary condition exactly. Numerical example demonstrates the effectiveness of the method in superplastic forming.