Abstract: The fracture reasons of outside race in bearing was analyzed by chemical composition analysis,metallographic microstructure examination,macro and micro-fractography. The results showed that the main fracture cause of outside race in bearing was not mounted properly,and outside surface happened to wear and burn badly. And the impact ductility was declined and the expansion of crack and the fracture was accelerated because of the reticulate carbonide of interruption being in material microstructure.