A method and a device for realizing dynamic adjustment of data bandwidth of the invention are disclosed. The method comprises adding a control channel in a PCM trunk link to describe occupancy condition of time slots for current services. The device comprises a control word process circuit, a time slot distribution circuit and a CPU interface circuit, wherein the control word process circuit is designed to complete abstraction and insertion of control information in a control channel of E1/T1 link, the time slot distribution circuit completes separating voice time slots from Ethernet data time slots and rebuilding the data, and the CPU interface circuit implements time slot distribution control. The method and the device can implement dynamic adjustment of Ethernet data bandwidth while ensuring voice services, to make effective use of trunk bandwidth and enhance user's data service bandwidth, and there is no error code and interruption of data service during bandwidth adjustment.