A communication method, characterized by , comprising: when two of the following conditions are satisfied: a system bit error rate is lower than a preset threshold, and a quantity of subcarriers, on which signal to noise ratio, SNR, degradation occurs, in an optical signal exceeds a predetermined numerical range, determining , by a receive end according to an SNR of a to-be-adjusted subcarrier, modulation order information and power information that correspond to the to-be-adjusted subcarrier, wherein the to-be-adjusted subcarrier is at least one subcarrier in the subcarriers on which SNR degradation occurs; sending , by the receive end, a trimmer request message to a transmit end, wherein the trimmer request message comprises the modulation order information and the power information that correspond to the to-be-adjusted subcarrier; receiving , by the receive end, an effective time point sent by the transmit end; wherein, the receiving, by the receive end, an effective time point sent by the transmit end comprises: receiving, by the receive end, a trimmer response message sent by the transmit end, wherein the trimmer response message comprises the effective time point; wherein, the trimmer response message further comprises a response flag bit, and the response flag bit is used to indicate whether the transmit end performs modulation on and power allocation for the to-be-adjusted subcarrier according to the modulation order information and the power information that correspond to the to-be-adjusted subcarrier; and receiving , by the receive end, a subcarrier at the effective time point by using a demodulation order corresponding to the to-be-adjusted subcarrier, wherein the demodulation order corresponding to the to-be-adjusted subcarrier corresponds to a modulation order corresponding to the to-be-adjusted subcarrier. when two of the following conditions are satisfied: a system bit error rate is lower than a preset threshold, and a quantity of subcarriers, on which signal to noise ratio, SNR, degradation occurs, in an optical signal exceeds a predetermined numerical range, determining , by a receive end according to an SNR of a to-be-adjusted subcarrier, modulation order information and power information that correspond to the to-be-adjusted subcarrier, wherein the to-be-adjusted subcarrier is at least one subcarrier in the subcarriers on which SNR degradation occurs; sending , by the receive end, a trimmer request message to a transmit end, wherein the trimmer request message comprises the modulation order information and the power information that correspond to the to-be-adjusted subcarrier; receiving , by the receive end, an effective time point sent by the transmit end; wherein, the receiving, by the receive end, an effective time point sent by the transmit end comprises: receiving, by the receive end, a trimmer response message sent by the transmit end, wherein the trimmer response message comprises the effective time point; wherein, the trimmer response message further comprises a response flag bit, and the response flag bit is used to indicate whether the transmit end performs modulation on and power allocation for the to-be-adjusted subcarrier according to the modulation order information and the power information that correspond to the to-be-adjusted subcarrier; and receiving , by the receive end, a subcarrier at the effective time point by using a demodulation order corresponding to the to-be-adjusted subcarrier, wherein the demodulation order corresponding to the to-be-adjusted subcarrier corresponds to a modulation order corresponding to the to-be-adjusted subcarrier. <EOS>