A method that can generate ultra-wide and flat noise in the whole millimeter-wave band is proposed. Based the vernier effect, the frequency intervals and incoherent light widths of the main ruler and the subordinate ruler are designed by using two incoherent optical frequency combs with different frequency intervals. Simulation results show that the proposed method can generate ultra-wide band and flat full-band millimeter-wave white noise with a frequency range of 30-300 GHz. Experimentally, the amplified spontaneous emission noise is filtered out of two comb-shaped lights with a vernier frequency interval through a programmable filter, and two millimeter-wave white noises are achieved based on uni-traveling-carrier photodetector with two different band widths. The frequency ranges of the two white noises are 130-170 GHz and 280-380 GHz, and the corresponding flatness are ±2.25 dB and ±3.10 dB, which verifies the correctness of the proposed theory.