The invention discloses a device and method for generating eight frequency multiplication millimeter waves by utilizing a Mach-Zehnder modulator, and the device and method are mainly used for the generation of the optical millimeter waves in a radio over fiber (ROF) access network. The method is shown in attached figures: optical millimeter wave signals, the frequency of which is eight times as large as that of local oscillator signals, are generated by utilizing nonlinear characteristics and interference superposition characteristics of two parallelly-connected double-parallel lithium niobate Mach-Zehnder modulators (DPMZM) and under the condition of an appropriate DC bias voltage, thereby greatly reducing equipment frequency index required for generating high frequency/ extremely high frequency signals, and reducing the system cost. According to the device and method, specific phase modulation index is not needed, and radio-frequency signals can be flexibly adjusted, so that the requirement for radio-frequency power is lowered; and meanwhile, stray sideband can be well restrained.