Abstract: For the full-decarburized layer of SCM435 wire rod in the production process, the billet after heating, rolled pieces and the finished wire rod were tested for microstructure analysis. The results indicate that slow cooling after spinning is the reason for formation of full- decarburized layer of SCM435 wire rod. By optimizing the cooling process of increasing the running speed of Stelmor cooling roll to 14.5-20 m/min，the cooling time of the wire rod in the insulation cover is reduced from 410 s of the original process to 283 s and the cooling rate is increased by about 0.3℃/s, the full-decarburized layer of the rod disappears.