Abstract: Fracture was found in the split pin of the engine, which joint alone the course left α1 cylinder and the bracket fixed pin. After the check of an engine breakdown, the mode and cause of the fracture were analyzed by appearance observation, macro and micro observation on the fracture surface, chemical composition analysis, metallographic examination, hardness test, and finite element analysis. The results show that the material hardness value of fault split pin is too high, which does not meet the standard requirement; the fracture of the split pin is fatigue fracture, and the reason for fatigue fracture is in the process of the engine working, and there is circumferential friction on the surface of the fault split pin and the side surface of the cylinder, the inner act surface of the split pin creates the bending stress and the wear on the surface near the source area.