Abstract: The connecting rod of a certain car engine broke during the factory testing process. The reasons for the fracture of the connecting rod were analyzed using macroscopic observation, scanning electron microscopy and energy spectrum analysis, metallographic examination, chemical composition analysis, hardness testing. The results show that the residual protective slag on the surface of the original steel billet caused the smallest plastic deformation at the small head hole of the connecting rod to break first. The connecting rod underwent long-term high-temperature oxidation during the heating process before forging, and the cracks continued to propagate, resulted in insufficient bearing capacity of the small head hole and ultimately led to overload fracture of the connecting rod body.