A data transmission method, wherein the method is performed by a system comprising a source distributed unit, DU, a centralized unit, CU, and a target DU, the method performs switching of a UE from the source DU to the target DU, the source DU and the target DU are controlled by the CU, the method comprises constructing, by the source DU, a packet data convergence protocol, PDCP, transmission status report based on transmission status of downlink PDCP protocol data unit, PDU, data sent by the source DU and a radio link control, RLC, status report fed back by the UE ; reporting, by the source DU, the PDCP transmission status report to the CU, wherein the PDCP transmission status report enables the CU to determine PDCP protocol data unit, PDU, data which is not successfully received by the UE; receiving, by the CU, the PDCP transmission status report, acquiring, by the CU, the determined PDCP PDU data which is not successfully received by the UE according to the PDCP transmission status report and retransmitting, by the CU, the acquired determined PDCP PDU data to the target DU; receiving and caching, by the target DU, the determined PDCP PDU data sent by the CU in advance ; transmitting, by the CU, a RRC reconfiguration instruction to the UE via the source DU, and informing, by the CU, the UE to perform DU switching ; after the switching from the UE to the target DU is completed, receiving, by the target DU, a triggered PDCP status report from the UE, wherein the triggered PDCP status report informs the target DU of PDCP PDU data which is not successfully received by the UE ; and retransmitting, by the target DU, from the determined PDCP PDU data cached, the PDCP PDU not successfully received by the UE to the UE according to a content of the triggered PDCP status report constructing, by the source DU, a packet data convergence protocol, PDCP, transmission status report based on transmission status of downlink PDCP protocol data unit, PDU, data sent by the source DU and a radio link control, RLC, status report fed back by the UE ; reporting, by the source DU, the PDCP transmission status report to the CU, wherein the PDCP transmission status report enables the CU to determine PDCP protocol data unit, PDU, data which is not successfully received by the UE; receiving, by the CU, the PDCP transmission status report, acquiring, by the CU, the determined PDCP PDU data which is not successfully received by the UE according to the PDCP transmission status report and retransmitting, by the CU, the acquired determined PDCP PDU data to the target DU; receiving and caching, by the target DU, the determined PDCP PDU data sent by the CU in advance ; transmitting, by the CU, a RRC reconfiguration instruction to the UE via the source DU, and informing, by the CU, the UE to perform DU switching ; after the switching from the UE to the target DU is completed, receiving, by the target DU, a triggered PDCP status report from the UE, wherein the triggered PDCP status report informs the target DU of PDCP PDU data which is not successfully received by the UE ; and retransmitting, by the target DU, from the determined PDCP PDU data cached, the PDCP PDU not successfully received by the UE to the UE according to a content of the triggered PDCP status report <EOS>