Overlapped selected mapping (OSLM) is a technique used to reduce the peak-to-average ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) system based on offset quadrature modulation (OQAM). The improved OSLM method is proposed to further reduce the PAPR based on the analysis of the traditional OSLM method. By changing the mode value of the phase rotation factor at some specific positions, this method can determine the side information at the receiving end, save spectrum resources in the OQAM/OFDM system and reduce PAPR of the system. The simulation results show that under the conditions of the same channel environment and a large number of subcarriers, this method can further reduce the PAPR of the system without increasing the bit error rate obviously.