Frequency-locking technology has greatly promoted the development of cavity ring-down spectroscopy in the field of spectral absorption. Therefore, cavity ring-down spectroscopy has gained advantages such as higher precision, better sensitivity, and increased stability. Based on the basic principles of classical cavity ring-down spectroscopy and frequency-locking technology, this paper reviews the current research status of frequency-locking technology in the field of absorption spectroscopy and its applications pertaining to atmospheric trace gases. This paper also lists several frequency-locking technologies that are widely used in the field of cavity ring-down spectroscopy. Finally, the application prospect of frequency-locking technology is determined combining the current development trend of frequency-locking technology and cavity ring-down spectroscopy technology.