A Chromatic Dispersion, CD, estimation method for an optical transmission network, the method comprising: converting data of two polarization states orthogonal to each other from time-domain data to frequency-domain data, performing extraction on the frequency-domain data and performing a linear combination operation on the extracted frequency-domain data, obtaining an argument of a CD value of the data of the two polarization states according to a result of the linear combination operation, and estimating the CD value according to the argument of the CD value of the data of the two polarization states; characterized in that the converting the data of the two polarization states orthogonal to each other from the time-domain data to the frequency-domain data comprises: converting the data of the two polarization states orthogonal to each other from the time-domain data to the frequency-domain data by adopting a discrete Fourier transform, with N = 2 t and t being a natural number which is greater than 2, and the frequency-domain data converted from the data of the two polarization states being set as X(k) and Y(k) respectively, k=0, 1,..., N-1, then Z k = ∑ n = 0 N − 1 z n W N nk, k = 0,1,..., N − 1, and Z k = X k + i ⋅ Y k, wherein i 2 = -1; where W N = e − j 2 π N, W N z(n) represents a sampled time-domain signal sequence, z(n)=x(n)+i·y(n), and consists of the data x(n) and y(n) of the polarization states in two dimensions orthogonal to each other, and Z(k) is a frequency-domain signal corresponding to the sequence z(n); wherein n=0, 1,..., N-1; wherein performing extraction on the frequency-domain data comprises: extracting data from the frequency-domain data according to the following rules: X U k = X k + N 4 − M 2, X L k = X k + 3 N 4 − M 2, and Y U k = X k + N 4 − M 2, Y L k = X k + 3 N 4 − M 2, where X U [ k] represents upper sideband data extracted from X(k), X L [ k] represents lower sideband data extracted from X(k), Y U [ k] represents upper sideband data extracted from Y(k), Y L [ k] represents lower sideband data extracted from Y(k), M = N 8, where k=0,1,...,M-1. converting data of two polarization states orthogonal to each other from time-domain data to frequency-domain data, performing extraction on the frequency-domain data and performing a linear combination operation on the extracted frequency-domain data, obtaining an argument of a CD value of the data of the two polarization states according to a result of the linear combination operation, and estimating the CD value according to the argument of the CD value of the data of the two polarization states; characterized in that the converting the data of the two polarization states orthogonal to each other from the time-domain data to the frequency-domain data comprises: converting the data of the two polarization states orthogonal to each other from the time-domain data to the frequency-domain data by adopting a discrete Fourier transform, with N = 2 t and t being a natural number which is greater than 2, and the frequency-domain data converted from the data of the two polarization states being set as X(k) and Y(k) respectively, k=0, 1,..., N-1, then Z k = ∑ n = 0 N − 1 z n W N nk, k = 0,1,..., N − 1, and Z k = X k + i ⋅ Y k, wherein i 2 = -1; where W N = e − j 2 π N, W N z(n) represents a sampled time-domain signal sequence, z(n)=x(n)+i·y(n), and consists of the data x(n) and y(n) of the polarization states in two dimensions orthogonal to each other, and Z(k) is a frequency-domain signal corresponding to the sequence z(n); wherein n=0, 1,..., N-1; wherein performing extraction on the frequency-domain data comprises: extracting data from the frequency-domain data according to the following rules: X U k = X k + N 4 − M 2, X L k = X k + 3 N 4 − M 2, and Y U k = X k + N 4 − M 2, Y L k = X k + 3 N 4 − M 2, where X U [ k] represents upper sideband data extracted from X(k), X L [ k] represents lower sideband data extracted from X(k), Y U [ k] represents upper sideband data extracted from Y(k), Y L [ k] represents lower sideband data extracted from Y(k), M = N 8, where k=0,1,...,M-1. wherein i 2 = -1; where W N = e − j 2 π N, W N z(n) represents a sampled time-domain signal sequence, z(n)=x(n)+i·y(n), and consists of the data x(n) and y(n) of the polarization states in two dimensions orthogonal to each other, and Z(k) is a frequency-domain signal corresponding to the sequence z(n); wherein n=0, 1,..., N-1; wherein performing extraction on the frequency-domain data comprises: extracting data from the frequency-domain data according to the following rules: X U k = X k + N 4 − M 2, X L k = X k + 3 N 4 − M 2, and Y U k = X k + N 4 − M 2, Y L k = X k + 3 N 4 − M 2, where X U [ k] represents upper sideband data extracted from X(k), X L [ k] represents lower sideband data extracted from X(k), Y U [ k] represents upper sideband data extracted from Y(k), Y L [ k] represents lower sideband data extracted from Y(k), M = N 8, where k=0,1,...,M-1.