Abstract: The morphology of line defect on the surface of 304 stainless cold rolled steel sheet is studied. The microscopic morphology of the line defect is investigated by use of optical microscope and scanning electron microscope (SEM) for analyzing the microstructures of the continuously casting slab, hot rolled strip and cold rolled sheet. The microscopic observation indicates the line defect on the surface of 304 stainless cold rolled steel sheet looks like a type of micro "groove", and there is oxide film at the edge of the groove. Some of the oxide film appears multilayer step structure, the oxidation film is made of chromic oxide and ferric oxide, and there are elements such as Mg, Ca, Al etc at the edge.