Abstract: Process parameters affect the temperature field and stress field of friction stir welding (FSW) welded joints, thereby affecting their fatigue performance. Exploring the relationship among “process parameters, field variation, and fatigue life” is of great significance for improving and regulating the fatigue life of aluminum alloy products. Based on numerical simulation methods, the variation rules of the temperature field and stress field of 5 mm-thick 7075-T6 aluminum alloy welded joints under different welding process parameters were analyzed, and Fe-safe software was coupled to explore the fatigue life changes. The results indicate that the temperature gradient \nabla f continuously expands from the nugget zone to the base metal zone, which leads to a more significant thermal strain difference, thereby continuously increasing the residual stress; the main influencing factor of temperature is the rotation speed of the stirring head, and the peak temperature increases by about 9% for every 100 r/min increase within the process parameters; the post-welding residual stress mainly manifests as longitudinal residual stress along the weld seam direction, and its value is directly proportional to the welding speed and inversely proportional to the rotation speed; at a low welding speed, the fatigue life of the welded joint is inversely proportional to the rotation speed, and the optimal process window is that the ratio K of the rotation speed to the welding speed is between 4 and 5, while the relationship with the welding speed is irregular. The above results are verified by experiments. They not only provide a theoretical basis for optimizing FSW process parameters but also offer technical guarantee and theoretical support for the promotion and application of 7075 aluminum alloy engineering structural components requiring a long service life, which has certain value and significance.