Abstract: The cardan shaft imbalance faults of CRH5 EMU (electric multiple unit) not only cause abnormal vibration and noise, but also reduce the service life of bearings. For some CRH5 EMU trains without onboard cardan shaft drive system monitoring device, based on the cardan shaft vibration transmission path, large number of field measured sample data are analyzed and the method for indirect judgement of cardan shaft imbalance fault using carbody floor vertical vibration state is proposed, as well as corresponding judgement standards. The carbody floor vertical 4065 Hz time-domain vibration acceleration wave filtering signal RMS (root mean square) value and the ratio of 40.65 Hz wave filtering signal in the original signal are used in this method as judgment indicators. Relevant test results show that the test method can effectively judge the cardan shaft imbalance fault.