In order to solve the requirement of positive real value of the signal at the light-emitting diode(LED) transmitting end in the optical orthogonal frequency division multiplexing(OOFDM) system, according to the characteristics of fast Hartley transform(FHT) "Real in Real out", FHT is used instead of fast Fourier transform(FFT), quadrature amplitude modulation(QAM) mapping is applied to FHT-based asymmetric limiting direct-current biased OOFDM system, and simulation experiments are carried out. The simulation results show that the FHT system has better bit error performance than the underwater visible OFDM communication system with the same frequency band utilization under the condition of the same underwater background noise.