Abstract: Tube mechanical expanding with conical die is investigated, the instability and wrinkling causes in expanding process are analyzed, and a unit mechanical model in deformation zone is established. Considering effects of work hardening in expanding process, rigid-plastic line hardening rule is adopted to describe the real stress-strain relationship. Analytic formula of the mechanical expanding is derived by slab method, and the numerical results indicate that the mechanical expanding force increases along with friction coefficients，while the die semi-cone angle exists an optimum value between 20° and 30° which can make the expanding force get a minimum value. Moreover, the optimum value increases along with friction coefficients, and the correctness of conclusions is proved by experiment investigation and numerical simulation.