Distributed optical fiber sensors based on optical time domain reflectometry （OTDR） perform characterization through spatially resolved measurements along a single continuous strand of optical fiber， which has major advantages on the technology and application costs compared with conventional point-type sensors. The conventional OTDR based on analog detection suffers performance limitations on the important parameters of spatial resolution and dynamic range of the system. In contrast， photon-counting OTDR by single photon detection can overcome these performance limitations through digital detection and recoding. This review focuses on the technologies employed and developments in photon-counting OTDR， aims to clarify the advantages and limitations of photon-counting OTDR， explores the future development trends， and promotes the further development of distributed optical fiber sensors based on OTDR.