Abstract. The finite element method (FEM) was used for simulation of piercing process of the tube in Diescher's mill. After a short description of the problem, the numerical model of the process was described. The simulated results visualize dynamic evolution of shear stresses and velocity in the piercing process. It shows that the distributions of shear stresses on the internal and external surface of the work-piece are mainly on the contact areas between the rolls and metal. The movement of mass points is not along circle direction but transverse. The reasons are analyzed. In conclusion, the position of plug should be located in the loose area and the discs should been arranged in a suitable position according to the ovalization of the workpiece forming.