The invention relates to an uplink and downlink channel reusing wavelength division multiplexing passive optical network system. The uplink and downlink channel reusing wavelength division multiplexing passive optical network system generates beat frequency power through a second photoreceiver, adjusts the wavelength of a second phototransmitter according to the beat frequency noise power so as to adjust difference between wavelengths of the second phototransmitter and a first phototransmitter, and reduces back Rayleigh scattering while colorlessness of OUN is guaranteed in uplink and downlink channel reusing communication equipment.