A scheme for generating 16-tupling millimeter wave signals is proposed, which uses parallel Mach-Zehnder modulators and optical attenuator without filters. In this scheme, the Mach-Zehnder modulator and optical phase shifter in parallel are used to generate the 8th-order optical sideband, and the 16-tupling millimeter wave signal is obtained through the beat frequency of photodetector. In view of ideal and non-ideal extinction ratio of modulator, when the extinction ratio is 35 dB and 100 dB respectively, the optical carrier and the fourth-order optical sideband are theoretically suppressed, and the eighth-order optical sideband signal is derived. The correctness of this deduction is verified by simulation. Furthermore, according to the simulation results, the influence of non-ideal conditions of various parameters, such as the shift of modulation index and optical attenuator attenuation value, the angle shift of electric phase shifter and optical phase shifter, on the system is analyzed. The 2.5 Gbit/s baseband signal is modulated on the 16-frequency millimeter wave signal generated by the scheme. When the transmission distance of the system is 5 km, 10 km and 15 km, the loss power is 0.35 dBm, 0.55 dBm and 2 dBm respectively, and the transmission loss is small. In addition, the relationship between laser linewidth and received power is analyzed. The received power is -22.6 dBm when the linewidth is 10 MHz, and the power losses are 0.1 dBm, 0.25 dBm and 0.6 dBm when the linewidth is 20 MHz, 30 MHz and 40 MHz, respectively.