The present disclosure relates to data transmission methods and apparatus to implement quality of service (QoS) flow-based data transmission in an architecture in which a central unit-control plane (CU-CP) and a central unit-user plane (CU-UP) are separated from each other. In one example method, when receiving data of a QoS flow, the CU-UP may send a QoS flow identity (ID) and a protocol data unit (PDU) session ID that are of the data of the QoS flow to the CU-CP, where a PDU session corresponding to the PDU session ID includes the data of the QoS flow.