Abstract: The crankshaft of a certain type of cliesel engine cracked during operation. The cause of crankshaft cracking was analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination, mechanical property testing, scanning electron microscopy and energy spectrum analysis. The results show that pitting corrosion occurred on the surface of the crankshaft under the action of corrosive medium containing sulfur, chlorine and other elements, and the corrosion pit at transition R became a fatigue source. Under the action of rotational bending and alternating stress, the corrosion pit cracked and expanded in a fatigue manner, ultimately led to crankshaft cracking.