In this paper, the control method of current gain compensation for welding is adopted. Precise current gain curves (i.e., current step curves) in resistance spot welding of galvanized steel plated are discussed and drawn. By analysis of failure of electrode cap, it indicates that new current step curve ensure that qualified welding spot nugget dimension is acquired. The welding spot is high in strength, stable and reliable in quality. It is superior to original current step curve.