In order to further improve the frequency mutiplication coefficient of photogenerated millimeter-wave in the radio over fiber (ROF) system,a scheme for generating frequency 20-tupling millimeter-wave signals based on the interaction of four Mach-Zehnder modulators (MZM) is proposed.The generation mechanism of frequency doubling scheme under ideal conditions is deduced.In the simulation experiment,the influences of DC bias voltage drift,modulation index and extinction ratio on the system performance under non-ideal factors are analyzed respectively.The results show that the saturation values of the optical sideband suppression ratio (OSSR) and the radio frequency spurious sideband suppression ratio (RFSSR) can reach 33.20 dB and 27.21 dB when the range of each parameter is set properly.For the ROF system based on this frequency doubling scheme,two different transmission modes of 2.5 Gbit/s data signal with single tone and dual tone modulation formats are compared and analyzed.The simulation results show that when the optical fiber distance is 40 km,the single sideband can still achieve error-free transmission,which reduces the influence of inter-code walk-off effect in the transmission process,increases the transmission distance of the system,and is more suitable for long-distance transmission.It provides a theoretical basis for the development of microwave photonics.