Abstract: Spot welding is the most important welding method in automotive industry, and the traditional main frequency spot welding machines has some shortcomings such as short life, energy waste, low power factor and poor quality stability. While the new intermediate frequency spot welding machines make up the defects of the traditional welding equipment. Based on the intermediate frequency welding machine with common plate, the effect of welding parameters on welding quality was studied. Combining with the actual production, data fitting, computing optimization, parameters ranges for different plates combinations were found. For different thickness combinations with different welding parameters, welded spot surface quality, microstructure and microscopic structure were studied. The engineering application shows that this method is convenient to find accurate and efficient parameters selection, especially in the new car project in the process of trial production and parameters optimization it has remarkable effects.