Abstract: In this paper, mathematical model of temperature field was set up through the heat conduction equation in the current skin effect.This process of solving was simplified, the results are accurate, the physical meanings are clear and directviewing.The results show that spot weld nugget is oval-shaped, therefore the current skin effect enlarges the spot welding area, thus increases its solidity and helps to curb the explosion of the spot weld nugget and splash.The results indicate that by changing the current frequency to adjust thickness of the current trend skin, the size of the spot weld nugget can be regulated.Under the guidance of the theory, the quality of the spot weld nugget can be improved, the structure of electrode is optimized and new weld machine is developed.The theoretical result has a great value in the engineering practice.