The embodiment of the invention provides a modulating method and device as well as a demodulating method and device of a GFDM (Generalized Frequency Division Multi-plex) signal. the modulating method comprises the following steps: acquiring an original signal to be modulated; shaping a pulse to obtain a random filter pulse; performing a cyclic convolution on a signal to be modulated sequence and the random filter pulse to obtain a first modulated signal; mapping the random filter pulse into a random phase sequence; returning a dot product of the first modulating signal and the random phase sequence for serving as a second modulating signal till circular times are up to a preset value; calculating a peak-to-average power ratio of each path of a time-domain signal; and determining a path of the time-domain signal with lowest peak-to-average power ratio as a modulated signal to be transmitted. As proved by the invention, through the pulse shaping and random phase sequence mapping, a path of the signal with the lowest peak-to-average power ratio can be determined as the signal to be transmitted, and the peak-to-average power ratio of the GFDM signal can be lowered remarkably.