Aimed at the cooling fan failures of CRH3 EMUs, combined the train vibration condition, conducted modal analysis andstrength analysis of the cooling fan were carried out based on the finite element software. Previous structure weak area was found accordingto the modals and stress distribution of the structure, which was in accordance with the actual failures. After reasonable improvement, thestructural strength of the fan support frame was increased, and at the same time, the natural frequency avoided the car-body resonance frequency.Finally, cracks on bolt hole were tested by ultrasonic, the testing results were good and able to distinguish the sizes and locations of the cracks.