The Excess Noise Ratio (ENR) of traditional noise sources is usually less than 20 dB due to the limitation of the working frequency and the power of electronic devices. To solve the problem, we propose a technology to generate a millimeter-wave noise source with a high ENR by two incoherent light beams beating. First, two optical filters are used to filter and shape the broadband amplified spontaneous emission light source. Then, the two obtained beams of amplified spontaneous radiation light with different frequencies are coupled to the photodetector for the beat frequency, which can generate electrical noise signals. A theoretical analysis predicts that a noise source with an ENR larger than 50 dB can be obtained by adjusting the optical spectral, linewidth and optical power of the two incoherent light beams filtered from an amplified spontaneous emission source under the current level of photodetector responsivity. A proof-of-concept experiment achieved a millimeter-wave noise source with an ENR higher than 50 dB. This method could also generate millimeter-wave and even terahertz-wave noise with a high ENR if a higher-speed photodetector was used.