The Aluminum has higher electric conductivity and thermal conductivity than iron.Welding of aluminum sheet is difficult because of low heating efficiency.Therefore,various joining methods are studied.One of the joining methods of the aluminum sheet includes friction stir welding or explosive welding.Magnetic pressure seam welding attracts attention as a new welding method [1]-[4].Magnetic pressure seam welding is a collision welding process,similar to explosive welding,utilizing electromagnetic force as the acceleration mechanism.Magnetic pressure seam welding uses electromagnetic force to accelerate one metal sheet(flyer plate)onto another stationary metal sheet(parent plate).Welding principle is shown in Fig.1.This paper deals with dynamic deformation process on magnetic pressure seam welding of aluminum sheets.Numerical analysis of the dynamic deformation process of the aluminum sheets is made by a finite element method.In this analysis,the aluminum sheets(100 mm width,1 mm thickness)were assumed to be composed of 20000 plane-strain quadrilateral elements.Discharge energy was each in 0.8kJ,1.0kJ and 1.2kJ.Gap length between flyer plate and parent plate was 1.0 mm.The result shows that when a collision angle becomes bigger than a constant value,the collision frictional stress increases.In addition,the increase in collision frictional stress is proportional to a collision angle.The maximum of the collision frictional stress is proportional to discharge energy.