The large-diameter seamless steel tube with thick wall is one of the foundation components of thermal power and nuclear equipment, and whose vertical extrusion process was simulated by the software of finite element simulation Deform-3D. The effective stress, effective strain and the load of top die were analyzed through changing the parameters such as extrusion ratio, die mould taper angle and so on. The simulation results show that with the increase of deformation degree, the effective stress and load of the blank increase gradually first and then reach a plateau. Along with the change of extrusion ratio and concave die taper angle, the equivalent stress, equivalent strain and load of top die have different changes. And when the extrusion ratio is 6 and cone angle is 30°, the forming pipe has the best quality.