Embodiments of the present invention provide a data forwarding method, device, and communications system, which relate to the field of communications and can achieve accuracy and continuity of data transmission during carrier aggregation for cells between base stations. The method includes: sending, by a primary base station, a first message to a secondary base station, where the first message is used to instruct the secondary base station to perform handover, and the first message includes an identifier of a target base station; confirming, by the primary base station, that the secondary base station forwards data to the target base station; and sending, by the primary base station, a second message to a user equipment, where the second message is used to instruct the user equipment to acquire the data from the target base station. The embodiments of the present invention are used for data forwarding.