In the light of the damage of axle box end cover on high speed train, First, the finite element model of the end cover is established for the modal analysis, where the intrinsic mode is captured at frequency around 580Hz. The results are verified by the later modal test and the comparisons with the field test data show that the intrinsic mode is quite close to the excitation frequency of 20-order wheel polygonalization. In response to this phenomenon, the vehicle multi-body dynamics model containing the axle box end cover is established by multi-body dynamics simulation software, and the vibration characteristic of the bolt and axle box end cover is analyzed. The simulation results show that the acceleration amplitude of axle box end cover is much larger than that of the axle box body. Furthermore, considering the spectrum analysis, the resonance of the end cover can cause the bolts to loosen, which probably happens when the preload drops to 2.5kN. The above conclusion is consistent with the test results, and another rule is found through the instrumented bolt: as the bolt preload decreases, the acceleration of end cover increases. This paper shows the reason of end cover destroy, and it is of great significance for the running safety of the high speed train.