Abstract: The crankshaft connecting rod of a marine diesel engine broke after running for 1 000 h. The fracture reasons of the connecting rod were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, roughness test and metallographic examination. The results show that the fracture property of the connecting rod was fatigue fracture, and the crack originated from the transition arc segment. The main reasons for the fracture was that the processing roughness at the transition arc segment was poor, and the local curvature was too large, which led to the increase of stress concentration at the point, thus causing the initiation and propagation of fatigue crack, and finally causing the connecting rod to fracture.