Non-linear distortion caused by excessively high peak-to-average power ratio(PAPR) is one of the problems to be sol-ved urgently in direct-current biased optical orthogonal frequency division multiplexing(DCO-OFDM) technology. Aiming at this problem, an algorithm based on time frequency interleaving(TFI) and selection mapping(SLM) which called TFI-SLM peak-to-average ratio suppression algorithm is designed. This algorithm firstly performs TFI on the input signal to reduce the autocorrelation of the input signal, and then uses a small m sequence to generate a random phase factor to selectively map the transformed signal. Simulation results show that compared with the traditional algorithm, the algorithm not only avoids sending too much redundant information of phase factor sequence, but also reduces PAPR by 2.8 dB when the complementary cumulative distribution function(CCDF) value is 10-5.