A method for determining precoding matrix for sub-band precoding, wherein the transmitter has two sets of cross-polarized antennas, the channel vectors of the two sets of antennas with different polarization direction are H 1 and H 2 respectively, these antennas are closely spaced, M is the amount of the transmitting antennas, r is the amount of the data flows, the channel vectors H 1 and H 2 of two sets of antennas satisfy the following complex relationship: H 2 = β e jδ H 1 Wherein β is the amplitude of the complex relationship between the two channel vectors, and δ is the angle of the complex relationship between the two channel vectors; the method comprises the following steps: a. determining, according to long-term channel related information, an optimized first matrix W 1 with a dimension of M×M, the first matrix corresponding to wideband and/or long-term channel properties, and the first matrix W 1 is selected from a first codebook below: W 1 = R 0 0 R, R = v 1 * e − jθ v 1 * ⋮ e − j M / 2 − 1 θ v 1 * = 1 e jθ... e j M / 2 − 1 θ e − jθ 1... e j M / 2 − 2 θ ⋮... ⋱ ⋮ e − j M / 2 − 1 θ...... 1 wherein, R is a proximity of the transmitting space correlation matrix of H 1, v 1 =[1, e -jθ,..., e - j ( M /2-1) θ] is a dominant eigenvector of the transmitting space correlation matrix of H 1, proximated by DFT vector, θ is the angle difference between the two neighboring items of the DFT vector; b. multiplying the optimized first matrix W 1 with each selected second matrix W 2 with a dimension of M×r in a second codebook, so as to obtain a plurality of candidate precoding matrices, wherein the second matrix W 2 corresponds to frequency-selective and/or short-term channel properties and is selected from second codebook below: W 2 = W 2 1, W 2 2,... W 2 r, wherein, W 2 i is the i-th column of W 2, letting n =└( i -1)/2┘+1, the n-th element of W 2 i is 1, and the (n+M/2)-th element is βe jδ when mod( i,2)=1, is 1/ βe - jδ when mod( i,2)=0 and other elements are 0; c. selecting an optimized one from the plurality of candidate precoding matrices for precoding the data to be transmitted based on predefined rules, according to the short-term channel properties. a. determining, according to long-term channel related information, an optimized first matrix W 1 with a dimension of M×M, the first matrix corresponding to wideband and/or long-term channel properties, and the first matrix W 1 is selected from a first codebook below: W 1 = R 0 0 R, R = v 1 * e − jθ v 1 * ⋮ e − j M / 2 − 1 θ v 1 * = 1 e jθ... e j M / 2 − 1 θ e − jθ 1... e j M / 2 − 2 θ ⋮... ⋱ ⋮ e − j M / 2 − 1 θ...... 1 wherein, R is a proximity of the transmitting space correlation matrix of H 1, v 1 =[1, e -jθ,..., e - j ( M /2-1) θ] is a dominant eigenvector of the transmitting space correlation matrix of H 1, proximated by DFT vector, θ is the angle difference between the two neighboring items of the DFT vector; b. multiplying the optimized first matrix W 1 with each selected second matrix W 2 with a dimension of M×r in a second codebook, so as to obtain a plurality of candidate precoding matrices, wherein the second matrix W 2 corresponds to frequency-selective and/or short-term channel properties and is selected from second codebook below: W 2 = W 2 1, W 2 2,... W 2 r, wherein, W 2 i is the i-th column of W 2, letting n =└( i -1)/2┘+1, the n-th element of W 2 i is 1, and the (n+M/2)-th element is βe jδ when mod( i,2)=1, is 1/ βe - jδ when mod( i,2)=0 and other elements are 0; c. selecting an optimized one from the plurality of candidate precoding matrices for precoding the data to be transmitted based on predefined rules, according to the short-term channel properties.