The invention provides an on-line rail vehicle bearing failure detection device and method. The device comprises a low-noise track located on a path by which a rail vehicle to be detected passes; a vibration sensing module comprising at least one vibration sensor unit and a signal output end and disposed on the low-noise track; a microphone module including at least one microphone unit and a signal output end and located at position at a side of the low-noise track and close to the vibration sensing module; and a data processing module including a signal input end and a signal output end, wherein the signal input end of the data processing module is connected with the signal output end of the vibration sensing module and the signal output end of the microphone module. The on-line rail vehicle bearing failure detection device and method can effectively improve the bearing failure detection rate and reduce the fault omitting probability of bearing failure.