To effectively solve the data transmission security and high peak-to -average power ratio (PAPR) caused by the orthogonal frequency division multipexing (OFDM) signals,this lett er proposes a chaos-based PAPR reduction and data encryption algorithm in orthogonal frequency division multiplexing-passive optical network (OFDM-PON) system.Firstly,the Lagrange polynomial is employed for the chaotic initial values hiding hence obtaining the secret keys protection.Then,the completely dynamic cipher texts are generated by the forward and backward XOR op erations,which can achieve the capacity of against chosen-plaintext attacks (CPAs).Finally,the chaos encrypt ed constant amplitude zero auto correlation (CAZAC) matrix multiplies with the OFDM signal vector to obtain the PAPR reduction.Experimental results show that,the proposed scheme can achieve ～2.4dB PAPR (PAPR=10－3) r eduction and ～1dB (BER=10－3) improvement of receiver sensitivity if com pared with the common OFDM-PON,which further improve the transmission performan ce.