A data transmission method, comprising: establishing, by a first base station, a first Packet Data Convergence Protocol, PDCP, entity; characterized by sending, by the first base station, first configuration information to a second communications node, and sending second configuration information to user equipment, so as to establish a second radio bearer between the second communications node and the user equipment, wherein the first configuration information comprises configuration information of a second PDCP entity of the second communications node, the second configuration information comprises configuration information of a fourth PDCP entity of the user equipment, and the second radio bearer corresponds to the second PDCP entity and the fourth PDCP entity; sending, by the first base station, fourth configuration information to the second communications node, so as to establish a third bearer between the first base station and the second communications node, and sending an association relationship between the second radio bearer and the third bearer to the second communications node, wherein the association relationship is used to associate the second radio bearer with the third bearer; and using, by the first base station, the third bearer and the second radio bearer to transmit at least a part of data of service data between the first base station and the user equipment, wherein the first PDCP entity of the first base station and the second PDCP entity of the second communications node perform joint processing on the at least the part of data, and performing, in the first PDCP entity, a sequence number processing function on the service data. establishing, by a first base station, a first Packet Data Convergence Protocol, PDCP, entity; characterized by sending, by the first base station, first configuration information to a second communications node, and sending second configuration information to user equipment, so as to establish a second radio bearer between the second communications node and the user equipment, wherein the first configuration information comprises configuration information of a second PDCP entity of the second communications node, the second configuration information comprises configuration information of a fourth PDCP entity of the user equipment, and the second radio bearer corresponds to the second PDCP entity and the fourth PDCP entity; sending, by the first base station, fourth configuration information to the second communications node, so as to establish a third bearer between the first base station and the second communications node, and sending an association relationship between the second radio bearer and the third bearer to the second communications node, wherein the association relationship is used to associate the second radio bearer with the third bearer; and using, by the first base station, the third bearer and the second radio bearer to transmit at least a part of data of service data between the first base station and the user equipment, wherein the first PDCP entity of the first base station and the second PDCP entity of the second communications node perform joint processing on the at least the part of data, and performing, in the first PDCP entity, a sequence number processing function on the service data.