Abstract: Friction stir welding(FSW) is a new solid-state joining process which was invented by The Welding Institute in 1991.FSW has been found to be effective for joining hard-to-weld metals and for joining plates with different thickness or different materials.2D numerical model was constituted in this paper and then the friction stir welding process was simulated.The parameters of FSW process,the flow of the material and the stress and strain in the FSW process were studied.Compared with the data of the experiments,numerical results were shown to demonstrate the efficiency and the validity of the model developed.