Abstract: Analyzed in the paper are the macroscopic morphology, microscopic morphology and electron spectrum of tube outer surface defects, so as to find out the causes for outer surface longitudinal defects in a Φ88.90 mm×6.45 mm, N80Q, flat end, non-upset tubing.The results show that the subsurface holes and the surface cracks in the tubing are respectively caused by the nonmetallic inclusions in the blank and the outer surface defects(surface reticular cracks or subsurface cracks).