Abstract: To improve the spot weld quality in the manufacturing process and study the factors effecting spot weld, a finite element model of DP780 with thickness of 1.6 mm and 2.0 mm was established, which was used to analysis the process of resistance spot welding. The strength indexes like failure shear force and nugget size are calculated by the model integrating force field, temperature field, electric field and microstructure. In addition, the welding nugget size was measured and failure shear force was also examined by using KSⅡ device. The numerical simulation results have errors of 2.05% and 13.6% compared to experiments, respectively. The errors are mainly caused by splash.