Abstract: The same welding parameters was after adopted to generate welding nuggets of different vehicle type,thickness and layer number in auto-body assembly process,which caused many welding defects. Aiming at the above problem,the resistance spot welding monitoring system with micro control unit as its core was introduced,which could achieve the functions of data acquisition,data transmission and nugget number based welding automatic adjustment technology. Based on the analysis of process parameters,the welding technology adjustment accuracy evaluation algorithm was established,which could guarantee each welding spot obtained under appropriate welding technology. The test results indicate that the developed system is stable,accurate and appropriate for practical application.