A signal transmission method includes using a signal integrating device to receive a first digital signal from a network line or to transmit a second digital thereto; feeding the power transmitted from the network line into the first digital signal to form an integrated signal; using a signal converting device to restore the integrated signal back to the network line power and the first digital signal; converting a first digital signal into a first analog signal or a second analog signal received from outside into a second digital signal; and using a coiled-wire cord connecting the signal integrating device and the signal converting device to transmit the integrated signal from the signal integrating device to the signal converting device or transmit the second digital signal from the signal converting device to the signal integrating device. The invention thereby achieves transmission of digital signals by a coiled-wire cord.