Numerical simulation was made on parameters like internal pressure and axial force as well as friction coefficient of tube that affect the formation of variable cross-section tube. Through numerical simulation and orthogonal optimization, the most thickness reduction ratio and thickness uniformity on different conditions were contrasted and analyzed. An optimum scheme was obtained and it could improve the formability of variable cross-section tube. The result indicates that the axial force plays the most important role on thickness reduction ratio. The result provides technical support for the variable cross-section tube hydroforming research.