Abstract: To investigate the impact of tool geometry on the temperature distribution in the core area of friction stir welding thick 2219 aluminum alloy plate, a three-dimensional simulation model of FSW 18 mm thick 2219 aluminum alloy is established based on ABAQUS/CEL.The finite element analysis method is applied to simulate the welding process and the real-time temperature cycle curve of the temperature measurement point in the core area of FSW is obtained.The temperature of the corresponding measurement points of the welding temperature field is detected by the developed thermocouple temperature measurement system, and the experimental and simulated data curves are basically the same at different rotation speeds, which verified the validity of the established simulation model.To explore the influence of the tool structure size on the core temperature field of the welding process, a four-factor, three-level orthogonal test is designed for the tool shoulder size, taper angle, shoulder concave angle, thread lift angle and other important details of the size.The results show that the shoulder diameter has the most significant effect on the temperature field difference of friction stir welding.When the shoulder size of the tool is 36 mm, the taper angle is 6°, the shoulder concave angle is 2.5° and the thread lift angle is 11°, the tool structure size is reasonable and the temperature field difference in the direction of the weld plate thickness is small.Highlights: The influence of tool geometry on the temperature field in the core area of friction stir welding is investigated, and the structural parameters of the tool are optimized.