Abstract: Because of high spectrum efficiency and robustness to multi-path delay, orthogonal frequency division multiplexing (OFDM) has been one of research hotspots in communication field. But the disadvantage of high peak-to-average power ratio (PAPR) in OFDM technology is one of the main obstacles to limit its wide applications. In order to reduce the peak-to-average power ratio of OFDM signals, the effective method that combined the selective mapping (SLM) technique with the irregular quasi-cyclic low density parity check (QC-LDPC) code is proposed, in which the irregular QC-LDPC code is selected as good error-correcting channel coding. The generated matrix of the irregular quasi-cyclic low density parity check code can be obtained directly with the two sub-matrixes in the parity check matrix. Compared with the traditional selective mapping technique, the combined method can give full play to advantages. By using the belief propagation (BP) iterative decoding algorithm of LDPC code, it can reduce the computational complexity and improve the decoding speed. The results with MATLAB simulation show that the proposed method can not only reduce the PAPR effectively and simply, but also have less affection to the bit error rate (BER) in orthogonal frequency division multiplexing system.