Abstract: The aluminum alloy sheets with TiO2powder addition were joined by resistance spot welding. The electrode voltage and welding current in the process of welding were detected in real-time to obtain the dynamic resistance curve of the nugget. Then the influence of TiO2powder on the resistance characteristics during the nugget nucleation and growth was analyzed. The results showed that the dynamic process of the nugget nucleation changed to present the different dynamic resistance. The three characteristic parameters, including contact resistance, final resistance and resistance heat of nugget nucleation extracted from the dynamic resistance curve could reflect the influence of TiO2powder on the nucleation quality. Moreover, the linear correlation between the final resistance, resistance heat of nugget nucleation and ultimate bearing capacity of the welding spot was established to evaluate the quality of the nugget nucleation.