Abstract <p>Titanium alloy is widely used in high-tech industries such as aerospace and military equipment due to its excellent properties. However, traditional welding methods for titanium alloy have many problems. Friction stir welding FSW is a solid-state welding technique that can reduce welding defects, but it also has limitations when applied to thick plates. DS-FSW has the potential to solve these problems. In this study, a DS-FSW thermo-fluid-solid coupling model was established using the CEL method in ABAQUS to investigate the thermal cycle, stress distribution, and material flow during the welding process. The effects of welding speed and tool rotation speed on the temperature field, stress field, and flow field were analyzed. The results show that increasing the welding speed can slightly reduce the peak temperature and optimize the heat input distribution. The stress increases with the welding speed due to the reduced heat input and insufficient material plasticization. The material flow speed vector distribution becomes more uniform with increasing welding speed. The tool rotation speed has a significant impact on the temperature field. Higher rotation speeds lead to higher peak temperatures and more uniform heat input distribution. However, excessive rotation speeds may cause the material to exceed the melting point, leading to welding defects. The stress decreases with the increase of the rotation speed due to the increased material plasticization and flow. The material flow speed vector distribution also becomes more uniform with increasing rotation speed. This study provides insights into the optimization of DS-FSW parameters for titanium alloy and contributes to the development of high-quality welding processes.</p>