Abstract: Bulging defects at the edge of strip steel forming during cold rolling process and corresponding measuring data are analyzed.It is concluded that local high spots at hot rolled strip steel are the major causes of the defects.In addition,convexity and wedge of the hot rolled plates and rolling length have certain influence on the formation of defects.Causes of local high spots are analyzed in the aspects of microstructure and rolling stress,and finally the bulging defects are noticeably reduced through process improvement.