Abstract: The formation causes for a kind of coarse particles on surface of hot-dip galvanized steel products were analyzed by instruments of optical microscope,scanning electron microscope and energy dispersive spectrometer,and corresponding preventive measures were proposed.The results show that coarse particles were resulted from the outburst microstructure which was generated by the extreme reaction of iron scraps and zinc bath.The iron scraps were caused by the scale press-in defect of the steel substrate.So the hot rolled descaling process should be controlled strictly in order to thoroughly remove the scales.