Abstract: A kind of automobile ring part was made by 4.0 mm 70 steel wire welded by resistance butt-welding. The cracks was found in the area of welding line of parts after polishing. The reason of cracks was analyzed by means of chemical composition analysis, hardness testing, fracture analysis and so on. The results showed that it was caused by the lack of chucking power of electrodes, the impurity had not been extruded fully, so there were remain some kinds of oxide in the parts. After adjusted the chucking power of electrodes, changed the shape of cutter and temperature of tempering, the cracks were eliminated and all the welding performances of part were met to the request of drawing.