Embodiments of this application disclose a data transmission method, including: sending, by a base station, first scheduling information to first UE, where the first scheduling information is used to instruct the first UE to send data to second UE based on the first scheduling information; receiving, by the base station, first feedback information sent by the first UE; and sending, by the base station, second scheduling information to the first UE if the first feedback information indicates that the second UE fails to receive the data. The embodiments of this application further provide a base station, UE, and a data transmission system.