In the motor industry, the number of spot welded points is closely related to overall cost of the vehicle assembly. A design based on experience is probable to lead redundant spot welded joints. Welded joints are critical in the structural performance, so it is hard to reduce the number. A measurable design index on the design of spot weld configuration is proposed in this study. We optimized the spot welding location and number in the lower control arm of the vehicle and automobile body, as far as the structure retained the structural stiffness. In order to ensure the requirements, we use a sizing optimization of each spot weld stiffness for the global structural rigidity. The survival index is defined the summation of resulted design variables, which is equal to the number of survival in the series of sizing optimizations. With this design index, one can optimally measure the importance of each spot weld joint and remove the redundant spot welds from the structure design.