The application of high strength steel sheets in automobile manufacturing has increased dramatically. To improve the joint performance of high strength steel sheet, an optimized RSW process was proposed. Double-pulse welding schedule was employed in the process. Under the second pulse current, the central temperature in the weld was higher than Ac3, and the second nugget was formed. The weld including two nuggets with different size and same center was obtained under the optimized process. By Vickers hardness analysis, the soft-hard alternating structure in the weld was formed. Under the same nugget size, the cross-tension strength of joints increase 30% by the optimized process. By comparison, the maximum tensile shear strength of RSW joints under dual-nugget process was higher than that under traditional heat treatment process. Furthermore, the temperature field under dual-nugget process was simulated and the weld thermal cycle of typical nodes in different weld regions were obtained. The simulation results explained the formation mechanism of the soft-hard alternating structure in the welds. The two ellipsoidal softening zones were formed respectively under different pulse welding currents.