The present disclosure relates to data transmission methods and apparatus. One example method includes receiving, by user equipment, a first message sent by a control plane network element or a user plane network element, where the first message includes a correspondence between a first quality of service identifier (NQI) and a first reflective quality of service identifier (RQI), obtaining, by the user equipment, a second message sent by the user plane network element, and if the second message does not carry a second RQI, generating, by the user equipment, a first quality of service rule based on the second message and the correspondence between the first NQI and the first RQI, where the second RQI is used to instruct the user equipment to activate a reflective quality of service (RQ) mechanism.