The impact defects on the surface of the axles of high-speed trains may cause hidden dangers to the safe operation of the trains. In order to study the influence of different shape defects on axle fatigue limit, the method of combining finite element simulation and fatigue test is adopted. According to the statistics of the foreign object damage impact defect of the axle in the workshop, impact defects were prefabricated on the axle specimen surface, stress analysis of the impact defect area was carried out, and then the more dangerous defect shape was obtained. Fatigue tests were carried out on prefabricated axle specimens. The P-S-N curves of each specimen group were fitted by the approximate Owen one-side tolerance limit method. In line with the fatigue test results of samples, considering the factors such as axle surface mass coefficient, size effect coefficient and load type, to ensure the security of the train operation, fatigue strength safety factor Sσ is introduced to establish a full-size axle fatigue prediction mathematical model. The fatigue limit of full-size axle with impact defects was predicted and the accuracy of the model was proved. Finally, on the basis of the defect shape, the modified EI Haddad model was used to fit the two-parameter theoretical model of defect depth and full-size axle fatigue limit, the standards were combined for safety assessment.