Abstract: In order to avoid welding defects resulting from the insufficient material flow and reduce the force during the welding process, semisolid friction stir welding (SSFSW) was put forward. Choosing 2024-T3 Al alloy as research object, the temperature and the microstructure were investigated. The results of temperature by numerical simulation and experiment show that at the rotational velocity of 1600r·min^-1 and the welding speed of 150mm/min, the peak temperature of materials in weld reaches 518℃ and excels the maximum temperature in solid state. Compared with the microstructure in weld zone of conventional friction stir welding joint under air cooling, the results of SSFSW joint under the water cooling show that the microstructure in weld zone is semisolid in which the grains tend to be globule and suspend in liquid.