［Purposes］It reviews the basic working principles, basic theories, and research progress of functional near-infrared spectroscopy (fNIRS) technology for detecting tissue blood oxygen saturation, providing reference for the future development of this technology in the medical field. ［Methods］Through literature review, the application of fNIRS technology in blood oxygen detection is summarized from the perspectives of detection principles, detection techniques, advantages and disadvantages. ［Results］On the basis of elucidating the basic principles of fNIRS technology for detecting blood oxygen, the principles and characteristics of three fNIRS detection technologies for blood oxygen, including continuous wave spectroscopy, frequency domain spectroscopy, and time-domain resolved spectroscopy were discussed, and their advantages and disadvantages were compared. ［Conclusions］The fNIRS technology has the advantages of good portability, non-invasive, high temporal and spatial resolution, and high tolerance for subjects’ actions. In the future, the propagation and distribution of photons in tissues can be analyzed by combining Monte Carlo method, so as to further deepen people’s understanding of the field of biomedicine Photonics and promote the application of fNIRS technology in medicine.