Abstract: In the process of cold drawing and subsequent finishing of steel pipe, the inner surface of steel pipe often appeared discrete distribution of pits, openings, cracks and other defects, which made the material scrapped and caused certain economic losses. The inner surface defects of various types of oil cylinder tubes were studied. The causes of the defects were analyzed and discussed by optical microscope and scanning electron microscope. The process that could cause the above irregular defects were found from the manufacturing process of the raw material tubes. The results show that the pit defect belonged to the foreign body indentation defect, which was caused by the falling off of the hard object in contact with the inner wall of the steel pipe. The notch defect was caused by the small infolding of the raw material pipe, the crack defects were related to the surface damage of the mandrel and the plug.