Using a single-fiber bidirectional system is an effective solution to the capacity expansion of the fiber-optic communication system and the simulation study of its performances is important to its practical applications.This paper presents an effective scheme

i.e.using the wavelength shifting technology to lower the reverse Rayleigh scattering in the system and using OptiSystem to set up a simulation model for the QPSK modulation-based bidirectional transmission system.When the transmitting power is 3dBm and the transmission distance is 360km

the Q factor of the proposed system is improved by 1.5times and the BER is reduced to 10-170 as compared with the traditional unidirectional WDM system.In addition

when the Q factor is over 6

the maximum transmission distance can reach 1 600km.Research results show that when the transmission capacity is the same

the bidirectional system can reduce the use of one fiber and its transmission performance is also somewhat improved.