Abstract: A heat source model of friction stir welding (FSW) was established, the temperature field during friction stir welding was simulated using finite element analysis software ABAQUS. The effect of welding speed, shoulder diameter of stirring tool and backing plate material on the temperature fields of welded pieces were investigated. It is shown that the peak temperature on welding pieces and duration at high temperature are reduced with the increase of welding speed. The friction heat between shoulder and welding pieces is the main source of heat input. The high- temperature distribution appearance at weld center with wider upper and narrower bottom becomes gradually more and more obvious with the shoulder diameter of stirring tool increasing. The backing plate material has significant effects on the temperature fields of the welding pieces and the weld quality. It is shown that appropriate welding parameters, dimensions of stirring tool and thermolysis conditions are very important for better weld quality.