Abstract: A series of study were carried out on the fractured connecting rod of rich gas compressor in coking unit of one oil refining factory by check analysis of chemical composition,microscopic structure,mechanical property and fracture microscopic observation. The results showed that the micro-crack was initiated in the role of the small end of compressor because of stress concentration under cyclic loading,then the micro-crack propagated,which at last leads to the fatigue fracture of small end of connecting rod.