Backscattering affects the performance of receivers in duplex underwater wireless optical communication (UWOC) systems. In this work, we study this issue using the Monte Carlo method. We show that with an increase of transmitter divergence angle, backscattering light power changes little while communication signal and optical signal-to-noise ratio (OSNR) are reduced dramatically at the receiver. With an increase of receiver field angle, backscattering light power becomes higher, communication signal is nearly unchanged, and OSNR is reduced greatly. With an increase of the separated distance between receiver and transmitter in each terminal, backscattering light power decreases quickly, communication signal is unchanged, and OSNR increases rapidly. With an increase of communication distance, backscattering light power is almost unchanged while both the communication signal and OSNR are reduced drastically. We demonstrate that, to reduce the impact of backscattering disturbance, the transmitter and receiver in each terminal should be placed at a greater distance and the latter should be with a smaller field angle. When the transmitting optical power or receiving sensitivity is too high, such disturbance is hard to suppress effectively. In this case, the system should work in half-duplex mode. These results will be useful for duplex UWOC system design. (C) 2018 Optical Society of America