The arc behavior of cold metal transfer technology in welding process and its effect on the appearance of weld are studied in details,and the micro-mechanism is also analyzed. The welding parameters such as welding voltage,welding current,wire feed rate and so on is controlled through integrated precision system,the micro-behavior of the welding arc are researched,the perfect combination of metal transfer physical behavior and welding parameters is achieved,which provides the theoretical base for obtaining high quality joining and appearance of welds,and also meets the design and welding demand for thin sheet covering parts of body-in-white. It has very important theoretical and practical engineering application value for enrichment and development of MIG welding method.