Single sided resistance spot welding (SSRSW) developed from resistance spot welding (RSW) is a feasible plan to join vehicle structure to closed-form tube and is increasingly used in automobile manufacturing. A ring spot weld can be formed between the two workpieces during this process. The weld strength is critical to the performance of vehicle. The mechanical property of the ring nugget, however, is lack of attention. In this study, a simulation model of workpieces with ring nugget for tensile-shear test was established and the stress and strain distributions around the weld were researched in detail. It was found that the maximum stress is generally concentrated at the out edge around the ring nugget. The failure region, however, may be in the heat affected zone (HAZ) instead of in the place of maximum stress, which should be judged by stress failure criteria (SFC) in the model. In addition, the tensile stress and shear stress on the surface of the lower sheet and upper tube were illustrated.