Stiffness designs of joints and major cross sectional members are a crucial step in a body structural design process. Traditionally, joints and cross sectional members are designed and optimized separately that potentially may result in some parts mismatching in geometry. The research objective is to develop a synchronized design optimization method of body joints and major cross sectional members to avoid this frequently encountered problem. The effectiveness of this optimization method is demonstrated with real world body design examples. The research method consists of four stages: (1) analyze a baseline joint for its stiffness performance, weight and cost; (2) optimize the joint design by maximizing its stiffness/weigh ratio; (3) conduct synchronized design optimization of the joint together with its adjacent cross sectional members for maximizing stiffness/weight ratio of the combined structure; and (4) compare stiffness performance, weight and cost between the optimized joints in stages 2 and 3 with the baseline joint. The synchronized design optimization method was successfully applied to new vehicle programs at Changan and resulted in significantly improved cost- and weight-efficient body structural designs with good stiffness performance. This optimization method has been implemented as part of a formal vehicle design and development process and will be applied to all major new vehicle programs at Changan. The synchronized optimization method provides a systematic method for achieving optimized conceptual designs of a body joint and its adjacent major cross sectional member with respect to stiffness, weight and cost efficiency. But the actual feasible engineering design of the connection between the two parts sometimes still presents a challenge. Further research is needed to explore feasible design alternatives for the connection designs. Regardless of the limitation of the research work, it still represents an innovative idea from the viewpoint of a practicing body design engineer. The application of the synchronized design optimization method does help design engineers achieve more effective body designs than those achieved with traditional optimization method.