There were many black strips on the steel surface after pickling of hot rolled strip. The surface microstructure and roughness of pickled steel were analyzed using SEM, EDS and surface roughness measurer. The experiment result showed that the microstructure was rugged and the surface roughness value was higher where the color was black, but there didn’t exist any element segregation. Combining with the research on oxide scale and simulated pickling of hot rolled plate in the laboratory, finally we got the key factors which led to the surface defect: the thickness uniformity of oxide scale on hot rolled plate and the combination state between oxide scale and steel substrate.