The invention discloses a method, a device and a system for enhancing line stability. The method comprises the following steps: while initiating, calculating the difference value between the power spectral density of the silence/noise state under the worst condition and the acquired power spectral density of the current silence/noise state; while initiating, calculating the sending power spectraldensity of a training signal according to the power spectral density interacted with the receiving end as well as the difference value; and in the showing stage, adjusting the sending signal of the current ith subcarrier according to the difference value, wherein i is a natural number. The sending end comprises a first calculating unit, a second calculating unit and an adjusting unit. The invention can not produce any power waste or speed loss, thereby saving the resources.