Abstract: As a revolutionary technology in low-photon imaging, first-photon imaging overcomes the reliance of traditional imaging on multi-photon accumulation by capturing the temporal statistical characteristics of the first photon of each pixel, realizes the ultra-efficient image reconstruction of one photon per pixel and provides a key solution for extreme scenarios such as ultra-low-light imaging and long-range remote sensing. This paper systematically reviewed the principles and research progress in first-photon imaging. Firstly, the hardware foundation of single-photon detection technology was introduced, including the core role of single-photon avalanche diode and time-dependent single-photon counting modules. Secondly, the fundamental principles of first-photon imaging were elaborated, covering the statistical modeling of first-photon signals and reconstruction methods of object reflectance and depth information. Then reviewed the research progress in this field including applications in target detection, first-photon ghost imaging, non-line-of-sight imaging and other related fields, as well as key breakthroughs in algorithm optimization and quantum imaging. Finally, the advantages and existing challenges of first-photon imaging technology were summarized, and the future development directions were prospected.