High peak-to-average power ratio (PAPR) of the signal is a major drawback in optical orthogonal frequency division multiplexing (OFDM) system. In this paper, an intensity-modulated type Partial Transmit Sequences (PTS) based scheme is proposed and applied to the intensity-modulated OFDM (IMDD-OFDM) system. The proposed intensity-modulated type PTS (IM-PTS) scheme ensures that the time-domain signal output by the algorithm is real value. What’s more, the complexity of the IM-PTS scheme has been reduced without much performance penalty. A simulation is performed to compare the PAPR of different signal. In the simulation, the PAPR of OFDM signal is reduced from 14.5 dB to 9.4 dB at 10−4 probability. We also compare the simulation results with another algorithm based on the PTS principle. A transmission experiment is conducted in a seven-core fiber IMDD-OFDM system at a rate of 100.8Gbit/s. The Error Vector Magnitude (EVM) of received signal is reduced from 9 to 8 at -9.4dBm received optical power. Furthermore, the experiment result shows that the reduction of complexity has little performance impact. The optimized intensity-modulated type PTS (O-IM-PTS) scheme effectively increases the tolerance of the nonlinear effect of the optical fiber and reduces the requirement for linear operating range of optical device in the transmission system. During the upgrade process of the access network, there is no need to replace the optical device in the communication system. What’s more, the complexity of PTS algorithm has been reduced, which lower data processing performance requirements of the devices such as ONU and OLT. As a result, the cost of network upgrades is reduced a lot.