Numerical simulation of temperature field on friction stir welded 7022 aluminum alloy was studied in this paper. A new dual-source model has been designed and applied to investigate the variation of temperature field over time. Result shows that temperature of the nodes along the welding line increased at first and then decreased, the highest nodal temperature of 524°C presents at the ending position. Temperature of the nodes perpendicular to the welding line rises rapidly when the source arrived and falls rapidly when it left, and then cools to room temperature linearly when the source is removed. Simulative result predicts large temperature difference on the plates, and thermal pretreatment should be conducted before welding.