The invention provides a millimeter wave generation method and an ROF system. The ROF system comprises a central station and a base station, wherein the central station comprises a first laser, a second laser, a first coupler, a first modulator connected with the first coupler, a radio-frequency signal source, a first filter, a first photoelectric detector, a second coupler, a DC block, a second modulator, a third modulator, a third coupler, a second filter connected with the third coupler, a third filter connected with the second filter, and an optical fiber amplifier connected with the third filter; the radio-frequency signal source and the first filter are connected with the first modulator; the first photoelectric detector and the second coupler are connected with the first filter; the DC block is connected with the first photoelectric detector; the second modulator and the third modulator are connected with the DC block and the second coupler respectively; the third coupler is connected with the second modulator and the third modulator; and the base station comprises a second photoelectric detector. The millimeter wave generation method and the ROF system have the advantages that the complexity of the base station is reduced; and generated millimeter waves are relatively high in degree of purity and quite low in error ratio.