A channel state information CSI feedback method, comprising: receiving a downlink symbol from a base station, wherein the downlink symbol comprises a pilot; obtaining a channel matrix based on the pilot comprised in the downlink symbol; calculating a precoding matrix based on the channel matrix and a basic codebook; generating CSI based on the precoding matrix; and transmitting an uplink symbol to the base station, wherein the uplink symbol carries the CSI; wherein an antenna array is configured for the base station, and the basic codebook is: W = W 1 W 2, wherein W is the basic codebook, W 1 is a beam codebook, a quantity of rows in the beam codebook is equal to a quantity of antennas of the base station, and W 2 is a weighted combining codebook; W 1 = G 0 0 G ′, G corresponds to a first group of antennas in the antenna array, and G' corresponds to a second group of antennas in the antenna array; and W 2 = A B, matrices A and B are both column vectors, quantities of non-zero elements comprised in the column vectors A and B are both greater than 1, a quantity of elements comprised in the column vector A is equal to a quantity of column vectors in a matrix G, and a quantity of elements comprised in the column vector B is equal to a quantity of column vectors in a matrix G', wherein the antenna array comprises 2N 1 N 2 antennas, both the first group of antennas and the second group of antennas comprise N 1 N 2 antennas, and G = g 1 g 2 ⋯ g M 1, g i ∈ Ω, 1 ≤ i ≤ M 1, 1 ≤ M 1 ≤ L, and G ′ = g 1 ′ g 2 ′ ⋯ g M 2 ′, g i ′ ∈ Ω, 1 ≤ i ≤ M 2, 1 ≤ M 2 ≤ L, wherein Ω is a preset group of (N 1 N 2 × 1) th -order vectors, the vectors are mutually orthogonal or not orthogonal, L is a quantity of vectors and L ≥ 2N 1 N 2, the column vectors in G are mutually orthogonal or not orthogonal, and the column vectors in G' are mutually orthogonal or not orthogonal; characterized in that W 2 = 1 1 + τ 2 A B, τ > 0, wherein T is a value of cross polarization leakage between a polarization direction of the second group of antennas and a polarization direction of the first group of antennas; A = β 1 β 2 ⋮ β M 1, β i ∈ δ, 1 ≤ i ≤ M 1, and δ = λ i e jφ i, 0 ≤ λ i ≤ 1,0 ≤ φ i < 2 π, M 1 ≤ i, wherein λ i and φ i are preset values, and ∑ i = 1 M 1 β i 2 = 1; and B = τe jθ η 1 η 2 ⋮ η M 2, 0 ≤ θ < 2 ⁢ π, η i ∈ σ, 1 ≤ i ≤ M 2, and σ = γ i e jφ i, 0 ≤ γ i ≤ 1,0 ≤ φ i < 2 π, M 2 ≤ i, wherein θ is an angle of phase rotation of the second group of antennas relative to the first group of antennas, γ i and φ i are preset values, and ∑ i = 1 M 2 η i 2 = 1. receiving a downlink symbol from a base station, wherein the downlink symbol comprises a pilot; obtaining a channel matrix based on the pilot comprised in the downlink symbol; calculating a precoding matrix based on the channel matrix and a basic codebook; generating CSI based on the precoding matrix; and transmitting an uplink symbol to the base station, wherein the uplink symbol carries the CSI; wherein an antenna array is configured for the base station, and the basic codebook is: W = W 1 W 2, wherein W is the basic codebook, W 1 is a beam codebook, a quantity of rows in the beam codebook is equal to a quantity of antennas of the base station, and W 2 is a weighted combining codebook; W 1 = G 0 0 G ′, G corresponds to a first group of antennas in the antenna array, and G' corresponds to a second group of antennas in the antenna array; and W 2 = A B, matrices A and B are both column vectors, quantities of non-zero elements comprised in the column vectors A and B are both greater than 1, a quantity of elements comprised in the column vector A is equal to a quantity of column vectors in a matrix G, and a quantity of elements comprised in the column vector B is equal to a quantity of column vectors in a matrix G', wherein the antenna array comprises 2N 1 N 2 antennas, both the first group of antennas and the second group of antennas comprise N 1 N 2 antennas, and G = g 1 g 2 ⋯ g M 1, g i ∈ Ω, 1 ≤ i ≤ M 1, 1 ≤ M 1 ≤ L, and G ′ = g 1 ′ g 2 ′ ⋯ g M 2 ′, g i ′ ∈ Ω, 1 ≤ i ≤ M 2, 1 ≤ M 2 ≤ L, wherein Ω is a preset group of (N 1 N 2 × 1) th -order vectors, the vectors are mutually orthogonal or not orthogonal, L is a quantity of vectors and L ≥ 2N 1 N 2, the column vectors in G are mutually orthogonal or not orthogonal, and the column vectors in G' are mutually orthogonal or not orthogonal; characterized in that W 2 = 1 1 + τ 2 A B, τ > 0, wherein T is a value of cross polarization leakage between a polarization direction of the second group of antennas and a polarization direction of the first group of antennas; A = β 1 β 2 ⋮ β M 1, β i ∈ δ, 1 ≤ i ≤ M 1, and δ = λ i e jφ i, 0 ≤ λ i ≤ 1,0 ≤ φ i < 2 π, M 1 ≤ i, wherein λ i and φ i are preset values, and ∑ i = 1 M 1 β i 2 = 1; and B = τe jθ η 1 η 2 ⋮ η M 2, 0 ≤ θ < 2 ⁢ π, η i ∈ σ, 1 ≤ i ≤ M 2, and σ = γ i e jφ i, 0 ≤ γ i ≤ 1,0 ≤ φ i < 2 π, M 2 ≤ i, wherein θ is an angle of phase rotation of the second group of antennas relative to the first group of antennas, γ i and φ i are preset values, and ∑ i = 1 M 2 η i 2 = 1. matrices A and B are both column vectors, quantities of non-zero elements comprised in the column vectors A and B are both greater than 1, a quantity of elements comprised in the column vector A is equal to a quantity of column vectors in a matrix G, and a quantity of elements comprised in the column vector B is equal to a quantity of column vectors in a matrix G', wherein the antenna array comprises 2N 1 N 2 antennas, both the first group of antennas and the second group of antennas comprise N 1 N 2 antennas, and