Abstract: In order to solve the problem of U71Mn steel rails fracture during straightening, microstructure, chemical compositions, mechanical properties and microhardness of fracture positions were observed and studied, respectively. The results show that the foreign inclusions, network cementite, acicular Widmanstatten cementite, the fine acicular martensite and micro cracks in corner of the steel rail because of friction impairment were main reasons for fracture of the U71Mn steel rails during straightening. At the same time, the solving measures were discussed.