Abstract: The internal combustion engine SAE1144 steel camshaft cracked during cold working. Use methods such as macroscopic observation, chemical composition analysis, metallographic inspection and fracture analysis to analyze causes of cracking of the camshaft. The results showed that the cracking of SAE1144 steel camshaft was laminar tearing. In the boring process, poor lubrication and misalignment of the axis of the camshaft caused excessive tangential stress on the turning tool, resulting in cracks at the interface between the sulfide and ferrite of the camshaft. The long strip of sulfide and ferrite layered strips in steel promoted the propagation of cracks. After the crack propagated, the camshaft cracked.