The invention discloses a data relay transmission method, a data relay transmission system and UE having a relay function. The method comprises the following steps of: receiving a UE data packet to be forwarded from the UE, and performing corresponding de-encapsulation and encapsulation processing of the UE data packet to obtain a first target data packet including first characteristic data, wherein the first characteristic data represents that the identity of the sender of the first target data packet is the UE; and then, sending the first target data packet to a mobile communication network node. Visibly, different from the existing relay scheme that relay data is sent through a role of a HeNB, the method disclosed by the invention is that the received UE data packet to be forwarded is sent after being processed into the target data packet capable of representing that the identity of the sender is the UE; namely, relay data is sent through a role of the UE in the method disclosed by the invention; the relay data can be directly transmitted to the mobile communication network node by using the relay UE in the method disclosed by the invention without an external network; the relay time delay is reduced; and the relay transmission reliability is improved.