A signal processing method, comprising: before a single end line test SELT signal is sent from a first user port, sending, by a digital subscriber line access multiplexer DSLAM, through the first user port, a crosstalk detection signal in a connected line, and receiving, by the DSLAM, through a second user port, an error sample E DS of an actual downlink signal fed back by a terminal side in a connected line, wherein the actual downlink signal comprises far-end crosstalk imposed by the crosstalk detection signal to the line connected to the second user port; wherein E DS is a set of errors between a quadrature amplitude modulation, QAM constellation point and a decision constellation point Ĉ DS corresponding to each subcarrier; wherein C DS is obtained by demapping a complex variable Z DS through constellation demapping, wherein the QAM constellation point is obtained by normalizing the Z DS; wherein the Z DS represents a frequency domain signal and each subcarrier in the line connected to the second user port corresponds to one frequency domain signal; and estimating, by the DSLAM, according to the error sample of the actual downlink signal and the crosstalk detection signal, a coefficient of a pre-coder of the DSLAM to obtain an estimated coefficient of the pre-coder, wherein the coefficient of the pre-coder is used to cancel far-end crosstalk on the line connected to the second user port when the first user port sends the SELT signal; wherein the estimating, according to the error sample of the actual downlink signal and the crosstalk detection signal, a coefficient of a pre-coder of the DSLAM comprises: C 0, k n + 1 = C 0, k n + u • E DS • z * wherein C 0,K represents a downlink crosstalk coefficient imposed to line 0 by line K in the pre-coder, n represents the n th iteration, u represents an iteration step of a least mean square algorithm, z* represents a conjugate of a crosstalk detection signal z sent by line K, and E DS represents the error sample of the actual downlink signal, wherein line K is a line connected to the first user port and line 0 is the line connected to the second user port. before a single end line test SELT signal is sent from a first user port, sending, by a digital subscriber line access multiplexer DSLAM, through the first user port, a crosstalk detection signal in a connected line, and receiving, by the DSLAM, through a second user port, an error sample E DS of an actual downlink signal fed back by a terminal side in a connected line, wherein the actual downlink signal comprises far-end crosstalk imposed by the crosstalk detection signal to the line connected to the second user port; wherein E DS is a set of errors between a quadrature amplitude modulation, QAM constellation point and a decision constellation point Ĉ DS corresponding to each subcarrier; wherein C DS is obtained by demapping a complex variable Z DS through constellation demapping, wherein the QAM constellation point is obtained by normalizing the Z DS; wherein the Z DS represents a frequency domain signal and each subcarrier in the line connected to the second user port corresponds to one frequency domain signal; and estimating, by the DSLAM, according to the error sample of the actual downlink signal and the crosstalk detection signal, a coefficient of a pre-coder of the DSLAM to obtain an estimated coefficient of the pre-coder, wherein the coefficient of the pre-coder is used to cancel far-end crosstalk on the line connected to the second user port when the first user port sends the SELT signal; wherein the estimating, according to the error sample of the actual downlink signal and the crosstalk detection signal, a coefficient of a pre-coder of the DSLAM comprises: C 0, k n + 1 = C 0, k n + u • E DS • z * wherein C 0,K represents a downlink crosstalk coefficient imposed to line 0 by line K in the pre-coder, n represents the n th iteration, u represents an iteration step of a least mean square algorithm, z* represents a conjugate of a crosstalk detection signal z sent by line K, and E DS represents the error sample of the actual downlink signal, wherein line K is a line connected to the first user port and line 0 is the line connected to the second user port.