A data transmission method, comprising: detecting (S402, 2), by a distributed unit, DU, of a source base station, a degradation of a link quality of a connection between the source base station and a terminal; sending, by the DU, a link quality degradation message to a centralized unit, CU, of the source base station, wherein the link quality degradation message carries a serial number of data successfully transmitted by the DU; in a case where the source base station is an anchor base station with a CU/DU separated architecture, and a target base station is an offload base station with an integrated architecture: stopping sending, by the CU, traffic downlink data to the DU, determining (S403, 5), by the CU of the source base station, data unsuccessfully transmitted by the DU according to the serial number, and sending, by the CU, the data unsuccessfully transmitted by the DU and all subsequent terminal traffic bearer data from the core network via a downlink data frame to the target base station, wherein a dual connection between the terminal, the source base station, and the target base station are established to perform offloading between the base stations; and the downlink data frame is used for the target base station to transmit the data unsuccessfully transmitted by the DU and all subsequence terminal traffic bearer data received from the core network to the terminal; in a case where the source base station is an offload base station with a CU/DU separated architecture, and a target base station is an anchor base station with an integrated architecture: sending (S404, 4), by the CU of the source base station, the link quality degradation message of the source base station to the target base station, wherein a dual connection between the terminal, the source base station, and the target base station are established to perform offloading between the base stations; and the link quality degradation message is used for the target base station to stop sending terminal traffic bearer data to the source base station, determine the data unsuccessfully transmitted by the DU according to the serial number, and send the data unsuccessfully transmitted by the DU and all of subsequent terminal traffic bearer data received from a core network to the terminal. detecting (S402, 2), by a distributed unit, DU, of a source base station, a degradation of a link quality of a connection between the source base station and a terminal; sending, by the DU, a link quality degradation message to a centralized unit, CU, of the source base station, wherein the link quality degradation message carries a serial number of data successfully transmitted by the DU; in a case where the source base station is an anchor base station with a CU/DU separated architecture, and a target base station is an offload base station with an integrated architecture: stopping sending, by the CU, traffic downlink data to the DU, determining (S403, 5), by the CU of the source base station, data unsuccessfully transmitted by the DU according to the serial number, and sending, by the CU, the data unsuccessfully transmitted by the DU and all subsequent terminal traffic bearer data from the core network via a downlink data frame to the target base station, wherein a dual connection between the terminal, the source base station, and the target base station are established to perform offloading between the base stations; and the downlink data frame is used for the target base station to transmit the data unsuccessfully transmitted by the DU and all subsequence terminal traffic bearer data received from the core network to the terminal; in a case where the source base station is an offload base station with a CU/DU separated architecture, and a target base station is an anchor base station with an integrated architecture: sending (S404, 4), by the CU of the source base station, the link quality degradation message of the source base station to the target base station, wherein a dual connection between the terminal, the source base station, and the target base station are established to perform offloading between the base stations; and the link quality degradation message is used for the target base station to stop sending terminal traffic bearer data to the source base station, determine the data unsuccessfully transmitted by the DU according to the serial number, and send the data unsuccessfully transmitted by the DU and all of subsequent terminal traffic bearer data received from a core network to the terminal.