The invention discloses a method for suppressing a peak-to-average power ratio in a grid multi-carrier parallel transmission system. By utilizing a principle of statistics, a companding signal is processed into an intercepted sharp distribution function with the distribution form same as the original signal, so that the statistical distribution properties of the original signal are maintained to the greatest degree, and the time-frequency characteristics of the transmitted aerial signal can be well guaranteed; and therefore, the error code performance loss caused by non-linear distortion can be effectively reduced. A simple and practical pre-distortion companding processing algorithm is adopted, and compression of a large signal in the transmitted signals and expansion of a small signal in the transmitted signals can be realized by changing the statistical distribution properties of the companding signal, so that high progressive consistency is realized between the distribution of the signal processed by a companding device and the distribution characteristics of the original signal. The test result proves that good time-frequency characteristics of the grid multi-carrier shaping impulse can be ensured when the peak-to-average ratio is effectively reduced, and the peak-to-average power ratio of the transmitted signal is obviously improved under the condition that the signal power is invariable before and after companding.