Abstract: In order to solve the problems of excessive dynamic balance and abnormal vibration of transmission system caused by improper bearing lubrication affecting driving safety during the usage of EMU cardan shaft, on\|board cardan shaft vibration monitoring device is developed. By installing vibration sensors on the gearbox and motor, the vibration signals in the cardan shaft frequency section of the gearbox and motor measurement point are taken as the characteristic quantity to monitor the cardan shaft health status in real time. According to the simulation analysis of measurement point acceleration response of the cardan shaft on different dynamic balance magnitude at different rotational speeds, the test verification of the platform, and the statistical analysis of the present vehicle vibration data of the EMU cardan shaft running on different lines, the on\|board alarm threshold is established and optimized, while on\|board early warning and alarm information according to fault classification are provided.