Single-atom catalysts (SACs) are gaining popularity in catalytic reactions due to their nearly 100 ​% atomic utilization and defined active sites, which provide great convenience for studying the catalytic mechanism of catalysts. However, SACs still present challenges such as complex formation processes, low loading and easy agglomeration of catalysts. Herein, we systematically discuss the synthesis methods for SACs, including co-precipitation, impregnation, atomic layer deposition, pyrolysis and Anti-Ostwald ripening etc. Various techniques for characterizing single-atom catalysts (SACs) are described in detail. The utilization of individual atoms in various photocatalytic reactions and their mechanisms of action in different reactions are explained. The purpose of this review is to introduce single-atom synthesis methods, characterization techniques, specific catalytic action and their applications in the direction of photocatalysis, and to provide a reference for the industrialization of photocatalytic single-atoms, which is currently impossible, in the hope of promoting further development of photocatalytic single-atoms.