With the rapid development of Chinese railways， the service reliability of rails has become increasingly important for the reduction of railway operation cost and improvement of operation safety. In this paper， a kind of cantilever structure is used to carry out the tests to study the vibration fatigue life and analyze its failure mechanism under different initial stress intensity factors when there is fatigue crack in U71Mn rail materials. The results show that the different initial stress intensity factors have great effect on the vibration fatigue life of U71Mn rails. By comparison， it is found that the propagation mechanism of vibration fatigue cracks in U71Mn rails is also different from the static fatigue. In the fatigue transient fracture zone， the vibration fatigue fractures have denser river patterns and larger and deeper dimples. In the fatigue crack propagation zone， when the initial stress intensity factor is large， the low-cycle fatigue damage mechanism dominates； when the initial stress intensity factor is small， the high-cycle fatigue damage mechanism dominates.