Disclosed are a channel state information (CSI) feedback method, a precoding method, and an apparatus. In the present invention, a terminal obtains, according to the number of downlink transport layers, a first precoding matrix set that is located on a first subband and that is corresponding to the number of the downlink transport layers, the first precoding matrix set comprising one or more precoding matrices, and a physical resource in the first subband being corresponding to a precoding matrix in the first precoding matrix set; the terminal determines a channel quality indicator (CQI) on a second subband according to downlink channel information and the first precoding matrix set on the first subband; and the terminal feeds back the CSI, the CSI comprising one or more of the following information: an RI used for indicating the number of the downlink transport layers, a PMI used for indicating the first precoding matrix set on the first subband and the CQI on the second subband. The technical solution disclosed in the resent invention can reduce signaling overheads of feeding back CSI by a terminal.