Disclosed are a data transfer method and system, and a UE having a relay function. The method comprises: receiving a to-be-forwarded UE data packet from a user equipment; obtaining a first target data packet comprising first characteristic data by correspondingly decapsulating or encapsulating the UE data packet, wherein the first characteristic data indicates that the identity of a sender of the first target data packet is the UE; and then, sending the first target data to a mobile communication network node. Accordingly, different from an existing relay solution in which transferred data is sent in a role of an HeNB, in the method of the present invention, a received to-be-forwarded UE data packet is processed into a target data packet capable of indicating that the identity of a sender is a UE, and the target data packet is sent, that is, the transferred data is sent in a role of the UE in the method of the present invention, so that the transferred data can be directly transmitted to a mobile communication network node by using a relay UE in the method of the present invention, and the aid of an external network is not required, thereby reducing the relay delay, and improving the reliability of the relay transmission.