The micro-ring resonator is an important device for the integration of silicon photonic chips. Based on the principle of micro-ring resonators, the paper mainly describes the research significance and development process of high-quality factor micro-ring resonators in the mid-infrared field, and analyzes the advantages and disadvantages of micro-ring resonators in different material systems in terms of technology and practical applications; then, we introduce the theoretical research of the cascaded micro-ring resonator based on the Vernier effect in the field of sensing and filtering in the mid-infrared region; the generation principle and development history of the mid-infrared Kerr optical frequency comb are reviewed, and we theoretically prove the germanium strip waveguide micro-ring can realize a wide-spectrum optical frequency comb with a bandwidth close to an octave at a pump power as low as 80 mW. Finally, we summarize the research progress and prospect the future applications.