A data transmission method, the method comprising: establishing, by a Relay Node, RN, a first correspondence relationship between a Multimedia Broadcast Multicast Service, MBMS, bearer identifier of an MBMS bearer of a Un interface between the RN and a donor eNB, DeNB, for an MBMS session and a user plane data tunnel identifier of the MBMS session and a second correspondence relationship between the user plane data tunnel identifier of the MBMS session and an MBMS session identifier of the MBMS session; and obtaining, by the RN, user plane data of the MBMS session received from a Donor eNB, DeNB, over an MBMS bearer of a Un interface between the DeNB and the RN determined by the DeNB according to the first correspondence relationship and transmitting the user plane data of the MBMS session to a User Equipment, UE, according to the second correspondence relationship; characterized in that, the RN establishes the first correspondence relationship comprises: receiving, by the RN, an MBMS Session Start Request message, carrying a Quality of Service, QoS, parameter of the MBMS session, received from the DeNB and obtain therefrom the user plane data tunnel identifier of the MBMS session; and in a process of establishing or updating an MBMS bearer of a Un interface triggered by the DeNB, obtaining, by the RN, the MBMS bearer identifier and establishing the first correspondence relationship between the MBMS bearer identifier and the user plane data tunnel identifier of the MBMS session; and feeding back an MBMS Session Start Response message to the RN; and the RN establishes the second correspondence relationship comprises: receiving, by the RN, an MBMS Session Start Request, carrying a Quality of Service, QoS, parameter of the MBMS session, received from the DeNB and obtaining therefrom the user plane data tunnel identifier of the MBMS session and the MBMS session identifier; and establishing, by the RN, the second correspondence relationship between the user plane data tunnel identifier of the MBMS session and the MBMS session identifier; and feeding back an MBMS Session Start Response message to the RN. establishing, by a Relay Node, RN, a first correspondence relationship between a Multimedia Broadcast Multicast Service, MBMS, bearer identifier of an MBMS bearer of a Un interface between the RN and a donor eNB, DeNB, for an MBMS session and a user plane data tunnel identifier of the MBMS session and a second correspondence relationship between the user plane data tunnel identifier of the MBMS session and an MBMS session identifier of the MBMS session; and obtaining, by the RN, user plane data of the MBMS session received from a Donor eNB, DeNB, over an MBMS bearer of a Un interface between the DeNB and the RN determined by the DeNB according to the first correspondence relationship and transmitting the user plane data of the MBMS session to a User Equipment, UE, according to the second correspondence relationship; characterized in that, the RN establishes the first correspondence relationship comprises: receiving, by the RN, an MBMS Session Start Request message, carrying a Quality of Service, QoS, parameter of the MBMS session, received from the DeNB and obtain therefrom the user plane data tunnel identifier of the MBMS session; and in a process of establishing or updating an MBMS bearer of a Un interface triggered by the DeNB, obtaining, by the RN, the MBMS bearer identifier and establishing the first correspondence relationship between the MBMS bearer identifier and the user plane data tunnel identifier of the MBMS session; and feeding back an MBMS Session Start Response message to the RN; receiving, by the RN, an MBMS Session Start Request message, carrying a Quality of Service, QoS, parameter of the MBMS session, received from the DeNB and obtain therefrom the user plane data tunnel identifier of the MBMS session; and in a process of establishing or updating an MBMS bearer of a Un interface triggered by the DeNB, obtaining, by the RN, the MBMS bearer identifier and establishing the first correspondence relationship between the MBMS bearer identifier and the user plane data tunnel identifier of the MBMS session; and feeding back an MBMS Session Start Response message to the RN; and the RN establishes the second correspondence relationship comprises: receiving, by the RN, an MBMS Session Start Request, carrying a Quality of Service, QoS, parameter of the MBMS session, received from the DeNB and obtaining therefrom the user plane data tunnel identifier of the MBMS session and the MBMS session identifier; and establishing, by the RN, the second correspondence relationship between the user plane data tunnel identifier of the MBMS session and the MBMS session identifier; and feeding back an MBMS Session Start Response message to the RN. receiving, by the RN, an MBMS Session Start Request, carrying a Quality of Service, QoS, parameter of the MBMS session, received from the DeNB and obtaining therefrom the user plane data tunnel identifier of the MBMS session and the MBMS session identifier; and establishing, by the RN, the second correspondence relationship between the user plane data tunnel identifier of the MBMS session and the MBMS session identifier; and feeding back an MBMS Session Start Response message to the RN.