A two-stage precoding method, comprising: sending, by a first device, first reference signals, wherein the first reference signals are used to estimate spatial correlation matrix information, wherein the first reference signals comprise a group of reference signals sent on a horizontal antenna array and a group of reference signals sent on a vertical antenna array; receiving, by the first device, spatial correlation matrix information from a second device; and determining, by the first device, a stage-1 precoding matrix in the two-stage precoding based on the spatial correlation matrix information; sending, by the first device, a second reference signal encoded by using the stage-1 precoding matrix, wherein the second reference signal is used to determine a stage-2 precoding matrix indicator; receiving, by the first device, a stage-2 precoding matrix indicator from the second device; determining, by the first device, a stage-2 precoding matrix based on the received stage-2 precoding matrix indicator; performing, by the first device, two-stage precoding on data by using the stage-1 precoding matrix and the stage-2 precoding matrix; and sending, by the first device, the data on which the two-stage precoding is performed; wherein the spatial correlation matrix information comprises a code word index of a first codebook and a code word index of a second codebook; wherein a code word R̂ 1 in the first codebook meets R̂ 1 = U ( ρ 1, n 1), and U ρ 1 n 1 = 1 ρ 1 ⋯ ρ 1 n 1 − 1 ρ 1 * 1 ρ 1 n 1 − 2 ⋮ ⋮ ⋱ ⋮ ρ 1 * n 1 − 1 ρ 1 * n 1 − 2 ⋯ 1, wherein ρ 1 = α 1 e jθ 1,(0≤ α 1 ≤1,0≤ θ 1 <2 π) represents a correlation coefficient of adjacent antenna elements in a single polarization antenna array in an antenna array, n 1 is a quantity of antenna elements in the single polarization antenna array, and the single polarization antenna array comprises antenna elements that are in a same row or a same column of the antenna array and that are in a same polarization direction; wherein a code word R̂ 2 in the second codebook meets: R ^ 2 = U ρ 2 n 2 β 1 e jφ 1 U ρ 2 n 2 β 1 e − jφ 1 U ρ 2 n 2 β 2 U ρ 2 n 2, wherein U ρ 2 n 2 = 1 ρ 2 ⋯ ρ 2 n 2 − 1 ρ 2 * 1 ρ 2 n 2 − 2 ⋮ ⋮ ⋱ ⋮ ρ 2 * n 2 − 1 ρ 2 * n 2 − 2 ⋯ 1, wherein ρ 2 = α 2 e jθ 2,(0≤ α 2 ≤1,0≤ θ 2 <2 π) represents a correlation coefficient of adjacent co-polarized antenna elements in a cross polarization antenna array in the antenna array, β 1, φ 1, and β 2 represent correlation between antenna elements in two polarization directions, wherein β 1 ≥ 0, 0 ≤ φ 1 < 2 π, and β 2 > 0, n 2 is a quantity of antenna elements in a same polarization direction in the cross polarization antenna array, and the cross polarization antenna array comprises antenna elements that are in the other of a same row or a same column of the antenna array and that are in two polarization directions. sending, by a first device, first reference signals, wherein the first reference signals are used to estimate spatial correlation matrix information, wherein the first reference signals comprise a group of reference signals sent on a horizontal antenna array and a group of reference signals sent on a vertical antenna array; receiving, by the first device, spatial correlation matrix information from a second device; and determining, by the first device, a stage-1 precoding matrix in the two-stage precoding based on the spatial correlation matrix information; sending, by the first device, a second reference signal encoded by using the stage-1 precoding matrix, wherein the second reference signal is used to determine a stage-2 precoding matrix indicator; receiving, by the first device, a stage-2 precoding matrix indicator from the second device; determining, by the first device, a stage-2 precoding matrix based on the received stage-2 precoding matrix indicator; performing, by the first device, two-stage precoding on data by using the stage-1 precoding matrix and the stage-2 precoding matrix; and sending, by the first device, the data on which the two-stage precoding is performed; wherein the spatial correlation matrix information comprises a code word index of a first codebook and a code word index of a second codebook; wherein a code word R̂ 1 in the first codebook meets R̂ 1 = U ( ρ 1, n 1), and U ρ 1 n 1 = 1 ρ 1 ⋯ ρ 1 n 1 − 1 ρ 1 * 1 ρ 1 n 1 − 2 ⋮ ⋮ ⋱ ⋮ ρ 1 * n 1 − 1 ρ 1 * n 1 − 2 ⋯ 1, wherein ρ 1 = α 1 e jθ 1,(0≤ α 1 ≤1,0≤ θ 1 <2 π) represents a correlation coefficient of adjacent antenna elements in a single polarization antenna array in an antenna array, n 1 is a quantity of antenna elements in the single polarization antenna array, and the single polarization antenna array comprises antenna elements that are in a same row or a same column of the antenna array and that are in a same polarization direction; wherein a code word R̂ 2 in the second codebook meets: R ^ 2 = U ρ 2 n 2 β 1 e jφ 1 U ρ 2 n 2 β 1 e − jφ 1 U ρ 2 n 2 β 2 U ρ 2 n 2, wherein U ρ 2 n 2 = 1 ρ 2 ⋯ ρ 2 n 2 − 1 ρ 2 * 1 ρ 2 n 2 − 2 ⋮ ⋮ ⋱ ⋮ ρ 2 * n 2 − 1 ρ 2 * n 2 − 2 ⋯ 1, wherein ρ 2 = α 2 e jθ 2,(0≤ α 2 ≤1,0≤ θ 2 <2 π) represents a correlation coefficient of adjacent co-polarized antenna elements in a cross polarization antenna array in the antenna array, β 1, φ 1, and β 2 represent correlation between antenna elements in two polarization directions, wherein β 1 ≥ 0, 0 ≤ φ 1 < 2 π, and β 2 > 0, n 2 is a quantity of antenna elements in a same polarization direction in the cross polarization antenna array, and the cross polarization antenna array comprises antenna elements that are in the other of a same row or a same column of the antenna array and that are in two polarization directions.