A bidirectional output signal frequency optional radio over fiber system based on coherent detection and digital signal processing technology is presented.The proposed system uses parallel phase modulator and wavelength selector switch structure.In the single source condition, the system realizes the baseband signal or multiple millimeter wave signal outputs for both the down and upstream transmissions.The simulation results prove that for the 20 Gbit/s 16-QAM modulated signal, through 30 km optical fiber transmission,the system output signal frequency of downlink can be selected from 0~60 GHz, and its transmission minimum error vector magnitude is 6.53%(0 GHz)~7.61%(60 GHz); the system output signal frequency of uplink can be selected from 0~120 GHz, and its transmission minimum error vector magnitude is 6.89%(0 GHz)~8.30% (120 GHz). The theoretical analysis and simulation results show that the full-duplex link can realize alternative frequency output, and maintains good performance.