To significantly bolster the security of data transmission in an orthogonal frequency division multiplexing passive optical network (OFDM-PON) system,we propose a digital sequence encryption scheme based on multi-chaotic system with multi-layer encryption scheme.By constructing chaotic sequence set with different chaotic system and using them for the various processing of OFDM signals′ generation,the encrypted key space of OFDM-PON system can be improved,which can enhance the confidentiality of system.Firstly,the transmitted data namely plaintexts would be grouped,and then by using the Logistic chaotic system to select the chaotic sequency from the chaotic sequency set to further perform the XOR operations with each set of plaintexts.Consequently,the encrypted data is injected into the 16-QAM (quadrature amplitude modulation) module. Secondly,the Logistic chaotic system is used to select the grouped-QAM signals and determine whether to encrypt the selected signals.Then,the subcarriers of the OFDM signals are grouped,and then are selected by the Logistic chaotic system to realize the encrypted operation.At last,the simulation experiment system is established to provide further validation of the feasibility of our scheme.And,the corresponding results show that,our scheme can present the good confidentiality,and 10540 key spaces can be achieved.