The present invention proposes a polar code-based optical OFDM signal coding modulation and demodulation system and method, the system includes a polar code coding unit, a high-order mapping unit, a subcarrier mapping unit, a pilot frequency acquisition unit, and an OFDM modulation unit , an optical transmitting and receiving unit, an OFDM demodulation unit, a subcarrier recovery unit, a high-order demapping unit, and a polar code decoding unit. User information is coded by polar code and then mapped to the corresponding carrier through high-order modulation. After IFFT, the conversion of frequency domain signal to time domain signal is realized, and then modulated onto the channel for transmission. The receiving end performs FFT on the signal, recovers the subcarrier signal, high-order soft demodulation and SC decoding of the polar code to restore the original user signal to realize the transmission of the entire system. The present invention combines polar codes with high-order modulation and carrier mapping, and can flexibly apply spectrum resources available in the system. The introduction of high-order modulation technology improves the transmission rate of information, and the introduction of polar codes improves the reliability of information transmission.