A full-duplex radio-over-fiber system with sextuple optical millimeter-wave generation transmit OFDM signal utilizing two parallel phase modulators is proposed.2.5 Gbit/s OFDM signal is modulated on the optical millimeter wave with 60 GHz frequency and transmitted to the base station over standard single-mode fiber(SMF).The generation principle and the transmission performance over fiber of optical millimeter wave generation are analyzed by theory and simulation,respectively.The results show that OFDM have more advantage than NRZ in ROF system.