Abstract:1235 cold-rolled plates with 7 mm in thickness and 1050 mm in width have been manufactured with electrolytic aluminum liquid, then cold-rolled into a thickness of 2.1 mm aluminum foil plates after 2 times of cold-rolled. Microstructure of surface black silk defects of cold-rolled plates with 2.1 mm in thickness were studied by optical microscopy (OM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), the formation causes of cold-rolled plates were discussed . The results show that there are some grooves in local surface black sill defect of cold-rolled plates, and coarse inclusions and second phase particles exist in the grooves, and the number of the grains in the surface black silk of annealed cold rolled plates is much smaller than that of the normal matrix. Spectrum results declare these coarse inclusions are non-metal oxide Al2O3 rich in Al and O elements, and the second phase particles are intermetallic compounds which are composed of Fe and Al elements with low content of Si elements, those inclusions and precipitates were reasons that cause black silk defect.