A signal transmission method using a polarization multiplexing coherence system, comprising the following steps: performing, by a transmitter, constellation mapping on a data stream to obtain a mapped signal; performing, by the transmitter, pre-filtering on the mapped signal to convert the mapped signal into a first filtered signal, wherein the pre-filtering is finite impulse response filtering, bandwidth of the first filtered signal is less than bandwidth of the mapped signal; performing, by the transmitter, waveform forming according to the first filtered signal to obtain a shaped signal; and performing, by the transmitter, digital-to-analog conversion on the shaped signal to obtain an analog signal, and sending, by the transmitter, the analog signal; performing, by a receiver, analog-to-digital conversion on the analog signal received by the receiver, to obtain a digital signal; performing, by the receiver, equalization and phase retrieval on the digital signal to obtain an equalized and retrieved signal; performing, by the receiver, post-filtering on the equalized and retrieved signal to convert the equalized and retrieved signal into a second filtered signal, wherein the post-filtering is finite impulse response filtering, and a bandwidth of the equalized and retrieved signal is greater than a bandwidth of the second filtered signal, wherein the post-filtering filters noise and introduces intersymbol interference corresponding to ISI introduced by the transmitter, wherein a formula for implementing the post-filtering is F k = W 0 ^ E k + W 1 ^ E k − 1 + ⋯ + W M − 1 ^ E k − M + 1, wherein k is a time sequence number, F ( k) is the second filtered signal, E ( k) is the equalized and retrieved signal, 0 ≤ j ≤ M -1, M -1 is a maximum delay amount based on a time unit, W j ^ is a j th filter coefficient, and E ( k - j) is a signal obtained by delaying E ( k) by j time units; wherein the maximum delay amount M -1 based on a time unit in the formula for implementing the post-filtering is equal to the maximum delay amount N -1 based on a time unit in the formula for implementing the pre-filtering, Ŵ j is determined by a pre-filter, where a manner of the determining is a training sequence manner or a noise spectrum analysis manner; and performing, by the receiver, sequence detection on the second filtered signal to obtain a sequence signal. performing, by a transmitter, constellation mapping on a data stream to obtain a mapped signal; performing, by the transmitter, pre-filtering on the mapped signal to convert the mapped signal into a first filtered signal, wherein the pre-filtering is finite impulse response filtering, bandwidth of the first filtered signal is less than bandwidth of the mapped signal; performing, by the transmitter, waveform forming according to the first filtered signal to obtain a shaped signal; and performing, by the transmitter, digital-to-analog conversion on the shaped signal to obtain an analog signal, and sending, by the transmitter, the analog signal; performing, by a receiver, analog-to-digital conversion on the analog signal received by the receiver, to obtain a digital signal; performing, by the receiver, equalization and phase retrieval on the digital signal to obtain an equalized and retrieved signal; performing, by the receiver, post-filtering on the equalized and retrieved signal to convert the equalized and retrieved signal into a second filtered signal, wherein the post-filtering is finite impulse response filtering, and a bandwidth of the equalized and retrieved signal is greater than a bandwidth of the second filtered signal, wherein the post-filtering filters noise and introduces intersymbol interference corresponding to ISI introduced by the transmitter, wherein a formula for implementing the post-filtering is F k = W 0 ^ E k + W 1 ^ E k − 1 + ⋯ + W M − 1 ^ E k − M + 1, wherein k is a time sequence number, F ( k) is the second filtered signal, E ( k) is the equalized and retrieved signal, 0 ≤ j ≤ M -1, M -1 is a maximum delay amount based on a time unit, W j ^ is a j th filter coefficient, and E ( k - j) is a signal obtained by delaying E ( k) by j time units; wherein the maximum delay amount M -1 based on a time unit in the formula for implementing the post-filtering is equal to the maximum delay amount N -1 based on a time unit in the formula for implementing the pre-filtering, Ŵ j is determined by a pre-filter, where a manner of the determining is a training sequence manner or a noise spectrum analysis manner; and performing, by the receiver, sequence detection on the second filtered signal to obtain a sequence signal.