The invention is specific to the problem of PAPR (peak to average power ratio) presented by OFDM (orthogonal frequency division multiplexing) modulation of 60 GHz millimeter wave communication system, and provides a method of lowering OFDM signal PAPR by using selectivity mapping combined with LDPC (low density parity check) to generate matrix high density character. By adding a little bit information, PAPR of the millimeter wave OFDM transmission signal is effectively lowered. In a big rate situation, a construction plan of improving an LDPC non-systematic code is provided, which can remarkably lower PAPR and effectively improve the transmission performance in the case of nonlinearity power amplifier distortion of 60 GHz millimeter waves system. Compared with the traditional coding scheme, the invention can remarkably lower PAPR, improve the transmission performance of millimeter wave signal in the presence of device nonlinearity and excels other coding scheme in aspect of anti-power amplifier PA nonlinearity. At the same time, the non-systematic code which is designed and constructed in the method and device can still have a fine performance when the coding rate is big. The arithmetic implementation of the non-systematic code is simple, and parallel computation can be used by the non-systematic code, so that the method and the device of lowering 60 GHz communication system PAPR (peak to average power ratio) based on LDPC (low density parity check) coding mechanism has great practical value in high-speed millimeter waves OFDM system.