The 3J53 steel wire was coiled into a spring and linear defect on the surface appeared after heat treatment. In this paper, the morphology of the linear defect of steel wire was analyzed by scanning electron microscopy. The linear defect was also analyzed by energy spectrum analysis, and the microstructure of the linear defect was observed by metallographic microscope. The results showed that the linear defect on the surface of steel wire was serrated and crack-type folding along the axial direction of steel wire. Folding defect was formed during the process of steel wire production, which was extended and stretched during the process of coiling and heat treatment, and eventually linear defect was formed.