The pursuit of clean and sustainable energy has become more urgent than ever. Photocatalysis is a promising approach to converting highly sustainable solar energy to promising fuels. Additionally, effective and robust cocatalysts are crucial factors in facilitating rapid photogenerated charge separation/charge transfer, widespread absorption and highly photoactive reaction and achieving efficient solar–to–chemical energy conversion. In this review, we summarize recent advances in efficient cocatalysts equipped with atomic metal sites including single–atom metal cocatalysts (SAMCs) and atomic cluster metal cocatalysts (ACMCs). First, we present a general definition of atomic metal sites to reinforce our understanding of the structure–activity correlations at atomic scale. Then, a brief description of advanced characterization techniques is given to distinguish the atomic metal sites. After introducing the atomic metal sites regulating strategies for the enhancement of photocatalysis, such as electronic metal–support interaction (EMSI), atomic alloy strategy and confinement strategy, the advantages and disadvantages of each kind of atomic metal sites and the solar energy conversion applications (water splitting, CO2 reduction, N2 reduction, etc.) are highlighted. Finally, the prospective and summary comparison of different atomic metal sites as well as the potential development direction of photocatalysts in the future are outlined.