Laser absorption spectroscopy (LAS) has the advantages of accurate quantification and straightforward operation. It has become the most widely used laser spectroscopic gas sensing technology. However, in many practical applications, traditional LAS cannot meet the requirements in high-precision optical path length measurement, multi-point gas sensing and large-dynamic-range detection. A spectroscopic gas detection method based on the frequency-modulated continuous-wave (FMCW) technique is introduced. In the method, FMCW is introduced into the LAS, and the absorption spectral information in optical FMCW signal is extracted while making full use of the high-precision positioning capability of FMCW. The basic principle of optical FMCW gas spectrum detection technology is introduced in detail firstly, then the latest research progress in synchronous measurement of gas absorption spectrum and optical pathlength, multi-point gas detection and large-dynamic-range gas detection is reviewed, and the future research work is prospected.