A data transmission method, wherein the method comprises: receiving, by a user plane function entity, a data packet from a first terminal through an uplink path corresponding to the first terminal, wherein the data packet carries addressing information of a second terminal; determining, by the user plane function entity based on an information about the uplink path corresponding to the first terminal, an identifier of a mobile local area network, MLAN, to which the first terminal subscribes; determining, by the user plane function entity based on the identifier of the MLAN and the addressing information of the second terminal, a downlink path corresponding to the second terminal; and sending, by the user plane function entity, the data packet to the second terminal through the downlink path corresponding to the second terminal; wherein the first terminal and the second terminal are in the same MLAN and correspond to the same user plane function entity; and wherein the information about the uplink path corresponding to the first terminal comprises a tunnel identifier of the user plane function entity that is allocated for the first terminal; and the information about the downlink path corresponding to the second terminal comprises a tunnel identifier of an access device that is allocated for the second terminal; wherein the determining, by the user plane function entity based on the identifier of the MLAN and the addressing information of the second terminal, the downlink path corresponding to the second terminal comprises: determining, by the user plane function entity based on the identifier of the MLAN, the addressing information of the second terminal, and a second correspondence, the downlink path corresponding to the second terminal, wherein the second correspondence comprises a correspondence between information about the downlink path corresponding to the second terminal, the addressing information of the second terminal, and the identifier of the MLAN; and wherein the method further comprises: obtaining, by the user plane function entity, the addressing information of the second terminal, wherein the addressing information of the second terminal comprises an internet protocol IP address of the second terminal, or a media access control, MAC, address of the second terminal. receiving, by a user plane function entity, a data packet from a first terminal through an uplink path corresponding to the first terminal, wherein the data packet carries addressing information of a second terminal; determining, by the user plane function entity based on an information about the uplink path corresponding to the first terminal, an identifier of a mobile local area network, MLAN, to which the first terminal subscribes; determining, by the user plane function entity based on the identifier of the MLAN and the addressing information of the second terminal, a downlink path corresponding to the second terminal; and sending, by the user plane function entity, the data packet to the second terminal through the downlink path corresponding to the second terminal; wherein the first terminal and the second terminal are in the same MLAN and correspond to the same user plane function entity; and wherein the information about the uplink path corresponding to the first terminal comprises a tunnel identifier of the user plane function entity that is allocated for the first terminal; and the information about the downlink path corresponding to the second terminal comprises a tunnel identifier of an access device that is allocated for the second terminal; wherein the determining, by the user plane function entity based on the identifier of the MLAN and the addressing information of the second terminal, the downlink path corresponding to the second terminal comprises: determining, by the user plane function entity based on the identifier of the MLAN, the addressing information of the second terminal, and a second correspondence, the downlink path corresponding to the second terminal, wherein the second correspondence comprises a correspondence between information about the downlink path corresponding to the second terminal, the addressing information of the second terminal, and the identifier of the MLAN; and wherein the method further comprises: obtaining, by the user plane function entity, the addressing information of the second terminal, wherein the addressing information of the second terminal comprises an internet protocol IP address of the second terminal, or a media access control, MAC, address of the second terminal. determining, by the user plane function entity based on the identifier of the MLAN, the addressing information of the second terminal, and a second correspondence, the downlink path corresponding to the second terminal, wherein the second correspondence comprises a correspondence between information about the downlink path corresponding to the second terminal, the addressing information of the second terminal, and the identifier of the MLAN; and wherein the method further comprises: obtaining, by the user plane function entity, the addressing information of the second terminal, wherein the addressing information of the second terminal comprises an internet protocol IP address of the second terminal, or a media access control, MAC, address of the second terminal.