Abstract: Cold heading steel is used to make the standard unit.The products tend to crack on the surface due to limited plasticity of materials.To improve properties of cold heading steel and product qualified rate,the cracking reasons of SWRCH35K bolt in the cold-heading process were investigated by acid washing,metallographical detection and energy spectrum analysis.Surface quality,metallurgical structure,crystal grain size and non-metallic inclusion were studied.The results show that surface folding defect of wire rod and segregation in the slab is the cracking reason for cold heading.At the same time the corresponding improving measures are put forward.