The problem of outer ring cracking and failure of tracd & needle roller bearing developed by a bearing factory in China was analyzed.By means of metallographic microscope,Vickers hardness tester and scanning electron microscope,the causes of bearing failure were analyzed from many aspects.The results show that the presence of reticulated carbides in the metallography of tracd & needle roller bearing of forging wheel greatly increases the brittleness of the material and makes the outer ring brittle crack rapidly under the action of external force during the operation of the bearing.From the fracture morphology analysis,brittle fracture is the main fracture,and plastic fracture is the secondary fracture.According to EDS analysis of scanning electron microscope,the main reason of brittle fracture of bearing outer ring is that the content of nitrogen element is too little，which lead by the loss of nitrogen compounds in the matrix and secondary precipitated phase.In conclusion,the cracking failure of the outer ring of tracd & needle roller bearing is caused by the existence of reticulated carbides and the loss of nitrogen content.