The invention discloses a method and a device for quantizing channel state information. According to the embodiment of the method and the device for quantizing the channel state information, the method that codeword indexes are provided for a base station from a user terminal is provided, the base station is provided with antennas, the number of the antennas is Nt, and the antennas are evenly arranged in a circular array. The method for quantizing the channel state information includes the following steps: according to an estimated wideband channel matrix, the user terminal determines a first codeword in a first codebook on the basis of a first predetermined rule, wherein the sequence of the first codebook is r, the first codeword is a group of beams for estimation of the wideband channel direction, and the r is equal to a positive integer from 1 to Nt; the codeword index of the first codeword is sent to the base station; for each subband, according to an estimated subband channel matrix, the user terminal determines a second codeword in a second codebook on the basis of a second predetermined rule, wherein the sequence of the second codebook is the r, the second codeword is used for describing the subband channel direction and is one wave beam in the first codeword; and then the codeword index of the second codeword is sent to the base station. Through the method and the device for quantizing the channel state information, a quite high system performance gain can be obtained at quite low PMI feedback cost.