Because of the wicked service environment of the high speed train,it is possible that the hollow axle of the train may encounter the foreign object damage and form a sharp notch.Under the fatigue loading a crack can initiate from the notch and propagate to failure.It is noted that the stress intensity factor is the control parameter of the crack propagating,for the purpose of getting the more exact propagation characteristics,the stress intensity factor is studied mainly.The service loads of hollow axles are defined,and the stress distribution of hollow axles is obtained according to the load spectrum.The semi-ellipse crack configuration is defined with three parameters:the aspect ratio,the relative depth and the relative location along the crack front.Quarter point 20-node isoparametric degenerate singular elements are used for the region near the crack tip.The finite element model of crack extension of hollow axle is created,and the crack front is dispersed which can realize orthogonal extension.Based on this the stress intensity factors of crack front were calculated,and the distribution rules of the stress intensity factors of different initial crack shapes are obtained.The conclusions are compared with that of the analytic method and they agree with each other very well,and the calculating results show that there is a close relationship between the stress intensity factor and the initial crack shape.For a round crack the stress intensity factor at the surface point increases faster than the one at the center point with the crack propagation.However,for a narrow crack,the results are in contrast with that of a round one.So,all the cracks with different shapes propagate toward to a similar shape,and they grow at this shape to end.The study may contribute to the crack propagate characteristics research. Because of the wicked service environment of the high speed train, it is possible that the hollow axle of the train may encounter the foreign object damage and form a sharp notch. Under the fatigue load of crack aint from the notch and propagate to failure. It is noted that the stress intensity factor is the control parameter of the crack propagating, for the purpose of getting the more exact propagation characteristics, the stress intensity factor is studied primarily. The service loads of hollow axles are defined, and the stress distribution of hollow axles is obtained according to the load spectrum. The semi-ellipse crack configuration is defined with three parameters: the aspect ratio, the relative depth and the relative position along the crack front. Quadrant point 20-node isoparametric degenerate singular elements are used for the region near the crack tip. The finite element model of crack extension of hollow axle is created, and the crack front is dispersed which can realize orthogon al extension.Based on this stress intensity factors of crack front were calculated, and the distribution rules of the stress intensity factors of different initial crack shapes are. The conclusions are compared with that of the analytic method and they agree with each other very well, and the calculating results show that there is is a close relationship between the stress intensity factor and the initial crack shape. For a round crack the stress intensity factor at the surface point increases faster than the one at the center point with the crack propagation. However, for a narrow crack, the results are in contrast with that of a round one. So, all the cracks with different shapes propagate toward to similar shapes, and they grow at this shape to end. The study may contribute to the crack propagate characteristics research.