The asymmetric thermo-physical mechanism of the resistance spot welding technique with intermediate frequency (2 kHz) and direct current (RSWIFDC) on the high strength aluminum (Al) alloy TL091 was studied here in view of the Peltier effect. On the basis of the analysis of the electrode cap surface erosion state and the shape-position of the nugget, it was concluded that asymmetric thermo-physical phenomenon occurred on both ends of the nugget, and even had an influence upon the shape-forming coefficient and the vertical position de-viation of the nugget, and the erosion degree of the electrode caps. In this work, the relative thermo-physical model of the welding was estab-lished combined with the Peltier effect and the spot welding characteristics. Accordingly the relative welding phenomena, such as nugget center deviation and different erosion degree of the electrode cap surface, was explained clearly using the model related with the Peltier ef-fect for the first time. This model provides important theoretical basis for future study and application of Al alloy spot welding, based on which, effective works may be done to promote the quality of the Al alloy welded joints and to obtain favorable control upon parameters of Al alloy welding for electrode caps.