This paper focuses on the problem of sheet metal cracking near the weld points in the side panel lock installation area of a new energy vehicle during the rear door opening and closing durability test (25,000 cycles). The rear half of the vehicle body is taken as the research object, and the fatigue stress distribution in this area is analyzed by combining tests with Finite Element Analysis (FEA). Aiming at the problem that the fatigue performance of the solder joint area is inferior to that of the general structural area, five improvement schemes centered on solder joint adjustment and structural adhesive addition are proposed. The durability performance of each scheme is evaluated through simulation analysis, and the optimal scheme is verified through bench tests. The results show that the hazardous areas identified by the finite element analysis are consistent with the crack areas in the test. The final selected scheme of "adding structural adhesive on the basis of the original scheme" reduced the stress of the side panel to 124MPa (lower than the elastic limit of 180MPa of DC06 cold-rolled steel plate), with over 50,000 test cycles, meeting the requirements of opening and closing durability, while also taking into account cost and process, providing a reference for similar body fatigue problems.