Abstract: According to the information provided by engineer,technicians and workers,there ex- ist four factors related to the existence of cracks'at the pressing place of vehicle axletree.i.e.  The rate of attenuation,the moving of the ware form,the width of the waveform and the height of the penetrating wave as the supersonic wave id being used to detecting cracks.To decide the possibility of crack existence(PCE),this article should firstly give the relationship between every one of the four factors and the PCE,respectively.Secondly,synthestically consider the degrees of influence of the four factors on the existence of crack,and finally determine the PCE.