A method for acquiring channel state information, comprising: a user equipment reporting codebook index information and information about a total number of layers ν to an eNode B (eNB), wherein the codebook index information comprises either: a second-class codebook index l or a first-class codebook index i and index parameter j wherein said second-class codebook index l includes said first-class codebook index i; after receiving the codebook index information and the information about the total number of layers sent by the UE, the eNode B obtaining a codeword in a manner of inquiring of a preset codebook list or in a manner of inquiring of the preset codebook list and combining with calculation according to the codebook index information and the information about the total number of layers, wherein a codeword is a precoding matrix; characterized in that, the step of obtaining the codeword comprises: when the codebook index information comprises i and j, the eNode B inquiring the preset codebook list using i, j and v as the index to obtain said codeword; and when the codebook index information comprises 1, the eNode B inquiring the preset codebook list using 1 and v as well as using i and v as the index to obtain said codeword; wherein, in the step of obtaining the codeword in the manner of inquiring of the preset codebook list and combining with calculation, a second-class codeword is obtained by way of a rotation algorithm or phase adjustment algorithm. a user equipment reporting codebook index information and information about a total number of layers ν to an eNode B (eNB), wherein the codebook index information comprises either: a second-class codebook index l or a first-class codebook index i and index parameter j wherein said second-class codebook index l includes said first-class codebook index i; after receiving the codebook index information and the information about the total number of layers sent by the UE, the eNode B obtaining a codeword in a manner of inquiring of a preset codebook list or in a manner of inquiring of the preset codebook list and combining with calculation according to the codebook index information and the information about the total number of layers, wherein a codeword is a precoding matrix; characterized in that, the step of obtaining the codeword comprises: when the codebook index information comprises i and j, the eNode B inquiring the preset codebook list using i, j and v as the index to obtain said codeword; and when the codebook index information comprises 1, the eNode B inquiring the preset codebook list using 1 and v as well as using i and v as the index to obtain said codeword; wherein, in the step of obtaining the codeword in the manner of inquiring of the preset codebook list and combining with calculation, a second-class codeword is obtained by way of a rotation algorithm or phase adjustment algorithm. when the codebook index information comprises i and j, the eNode B inquiring the preset codebook list using i, j and v as the index to obtain said codeword; and when the codebook index information comprises 1, the eNode B inquiring the preset codebook list using 1 and v as well as using i and v as the index to obtain said codeword; wherein, in the step of obtaining the codeword in the manner of inquiring of the preset codebook list and combining with calculation, a second-class codeword is obtained by way of a rotation algorithm or phase adjustment algorithm.