Disclosed in the present application are a method, an apparatus and a system for data transmission, which are used to realize support for transmission of MBMS service in a network scene with deployment of RNs. A data transmission method disclosed in the present invention comprises the following steps: a Relay Node RN establishes a first corresponding relationship between indications of Multimedia Broadcast Multicast Service MBMS bearers and indications of user plane data tunnels of MBMS sessions, and a second corresponding relationship between the indications of user plane data tunnels of MBMS sessions and indications of MBMS sessions; the RN obtains, according to the first corresponding relationship, the user plane data of a MBMS session transmitted from a Donor Evolved Node DeNB, and transmits, according to the second corresponding relationship, the user plane data of the MBMS session to a User Equipment UE.