Abstract: To analysis the causes of fatigue failure on the area around the traction motor seat of metro vehicle power bogie frames, the fatigue strength of the frame was calculated by using FEM. The calculated results show that the stresses on the area around the traction motor seat are mainly influenced by the vertical vibrations of traction motor. Increases in vertical vibration acceleration of the traction motor causes an increase in stress amplitudes of the dangerous nodes although it basically has no effect on the average stress of the node. When the vertical vibration acceleration of the traction motor increases from 1 g to 10 g, the stress amplitudes increases by about 1. 5 times, and the related safety factors decrease from over 2. 68 down to about 1. 00. The safety factors do not change with horizontal vibrations when they are within the ranges specified by specifications.