A baseband processing apparatus in a radio communication system, a radio communication system, and a baseband processing method. The apparatus includes a first unit and a second unit that implement different baseband processing functions, where the second unit is configured to generate a precoding matrix of a downlink coordinated multipoint transmission and reception (CoMP) user, generate precoding control information according to the precoding matrix, and send the precoding control information to the first unit; and the first unit is configured to receive the precoding control information sent by the second unit, and perform downlink joint baseband processing on downlink CoMP user data in downlink user data according to the precoding control information, so as to generate jointly sent baseband data for radio sending. The technical solutions can reduce transmission bandwidth between baseband processing units and obtain a system capacity gain at the same time.