Abstract: The welding structure design of rail transit vehicles is directly related to operational safety and service life. Through the establishment of stress analysis models for welded joints and fatigue-resistant design criteria, this paper proposes structural optimization schemes for critical locations such as the connection nodes between side beams and cross beams of bogie frames, and the lap joints of longitudinal and transverse beams in carbody underframes. Arc transitions are adopted to reduce stress concentration factors, appropriate butt welds and fillet welds are selected, and weld leg sizes and groove parameters are controlled. Finite element simulation and fatigue test results demonstrate that the optimized design reduces maximum stress by 28.5% and increases fatigue life by 85.7%. Engineering applications have verified the effectiveness of the design method, providing technical support for improving the reliability of vehicle components.