Abstract: In order to overcome the problem that the existing methods have a poor effect to reduce the Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) system in visible light communication. The analysis shows that the conjugate symmetry property enhances the correlation of the input sequence so that the PAPR performance of conventional methods significantly decreased in the Direct Currentbiased Optical-Orthogonal Frequency Division Multiplexing (DCO-OFDM) system. A novel method of combining Discrete Cosine Transform (DCT) and Grouping Cyclic Shift (GCS) to decrease the PAPR is proposed. Based on DCT, GCS of the proposed method could decrease the correlation of input sequence. So the system output signal would have a lower PAPR. Simulation results show that the proposed method is better to suppress the PAPR than when only using the DCT or GCS method. When the value of Complementary Cumulative Distribution Function is equal to 10^-4, the PAPR has decreased 5.4dB. DCT-GCS method has a low PAPR and the calculation complexity is much lower than the PTS and the SLM method.