This application discloses data transmission that includes: dividing to-be-transmitted content into a plurality of data units at a session layer; transmitting the data units to the target terminal device by using a first transmission channel as a responsible channel of the to-be-transmitted content; distributing, by the session layer in a case that the session layer switches the responsible channel of the to-be-transmitted content from the first transmission channel to a second transmission channel with a different transmission protocol, the data units to the second transmission channel; and transmitting the data units distributed by the session layer to the target terminal device through the second transmission channel. In data transmission in this application, the session layer controls switching of the channels and distribution of the data units, so that the transmission sequence is free from constraints of protocols and the degree of freedom in data transmission is increased.