Embodiments of the present invention provide a data transmission method, a base station, and a user equipment (UE), wherein a primary base station configures a data transmission parameter for a secondary base station, to assist the secondary base station to perform uplink and downlink data transmission for the UE. Therefore, the primary base station and the secondary base station transmit and receive data according to the same data transmission parameter, and there is no need to perform extra processing on the data transmitted and received by the secondary base station, that is, the secondary base station can only reserve simple buffering, encapsulating, and transceiving functions, or even only reserve buffering and transceiving functions, so that a protocol design of the secondary base station is simplified, and cost of the secondary base station, especially cost of a micro base station serving as the secondary base station is reduced.