A method for receiving Channel State Information (CSI) by a base station (BS) in a wireless communication system, includes receiving an encoded value for a specific CSI report mode, wherein the encoded value is joint encoded value of a rank indicator (RI) and a first precoding matrix indicator (PMI), obtaining the RI and a codebook index for the first PMI based on the encoded value, wherein the RI and the first PMI are jointly encoded into the encoded value in a way that following conditions are satisfied: when the encoded value is an integer ranging from 0 to 7, the RI is 1 and a codebook index for the first PMI is same as the encoded value, and when the encoded value is integer ranging from 8 to 15, the RI is 2 and the codebook index for the first PMI is the encoded value minus 8.