The invention provides a data transmission method used for supporting bandwidth extension. The data transmission method is characterized by comprising the steps of, in a downlink direction, carrying out resource mapping based on a to-be-extended effective bandwidth dw0 after a downlink signal is generated, carrying out antenna interface bandwidth matching after the mapping is finished, switching data after resource mapping to a time domain after the matching is finished and sending out the data through an antenna interface; and in an uplink direction, performing front-end processing of the matched interface bandwidth on the received signals, extracting effective frequency domain signal in the middle of the frequency band, and carrying out baseband service processing of a corresponding bandwidth by using the extracted signal. By adoption of the data transmission method, extension can be carried out based on the existing data transmission interface to satisfy different bandwidth requirements, the complexity of system design is reduced, and demands on hardware are reduced; meanwhile, the data transmission method is also adaptable to a special bandwidth. The data transmission method changes the system baseband processing little, and is low in complexity and easy to realize.