Embodiments of the present invention disclose a signal transmission method. A first correspondence is acquired between both a PSD of transmitted signals of the first communications equipment and a PSD of transmitted signals of a second communications equipment and a signal-to-noise ratio of received signals of the first communications equipment. A second correspondence is acquired between the signal-to-noise ratio of received signals of the first communications equipment and the number of bits for bearing signals. An optimization algorithm is used to calculate a PSD of transmitted signals of the first communications equipment and a PSD of transmitted signals of the second communications equipment.