Higher flexibility and high peak-to-average power ratio (PAPR) are the main challenges for orthogonal frequency division multiplexing passive optical network (OFDM-PON) systems. For this purpose, we propose a low PAPR OFDM-PON system with a dynamic regulatory factor U, which can dynamically adjust the transmission capacity of the system according to the needs of users at optical network units and reduce PAPR at the same time. Dynamic regulatory factor U can assign different probabilistic shaping schemes to different subcarriers, thus improving the system flexibility and adjustability in both the time and frequency domains. Meanwhile, U can flexibly change the number of phase sequence groups in selecting mapping, which is a well-known effective PAPR reduction technique. Simulations of a back-to-back OFDM-PON transmission system with different bit rates are setup to verify the performance of the proposed scheme. It is demonstrated that the proposed scheme achieves effective PAPR reduction performance with considerably lower computational complexity and outstanding bit error performance. More importantly, our proposed OFDM-PON system can be flexible and adjustable in acquiring different and dynamic access bit rates, which suggests a prospective solution for the next-generation PON.