A scheme of radio over fiber (ROF) system to generate 18-tuple frequ ency optical millimeter-wave by using a LiNbO₃Mach-Zehnder modulator (LN-MZM) and four-wave mixing in high ly nonlinear fiber (HNLF) is theoretically proposed and investigated by simulation.In the central station (C S),the ±3order sidebands are produced by properly adjusting the direct current bias and the modulation depth of the LN-MZM,and the phase difference of radio frequency (RF) signals.The baseband data is modulated on th e －3order sideband by the intensity modulator.Then the coupled ±3order sidebands are transmitted to the base station (BS) through fiber.In the base station,the coupled ±3order sidebands are sent to the HNLF,and ±9order sidebands are generated after four-wave mixing (FWM) effect.After optical filtering,an electrical millimete r-wave signal with 18-tuple frequency is obtained by beating frequency in the photoelectric detector.The si mulation result shows that the 60GHz optical millimeter-wave is generated by using 3.3GHz RF signal.The 2.5Gb/s data signal quality is still good after transmitted over 40km fiber.Furthermore,the effects of the input op tical power and the length of HNLF on the system performance are also investigated,and the optimal condition of th e system performance is obtained.