Single-atom catalysts (SACs), with atomically dispersed metal atoms anchored on a typical support, representing the utmost utilization efficiency of the atoms, have recently emerged as promising catalysts for a variety of catalytic applications. The electronic properties of the active center of SACs are highly dependent on the local environment constituted by the single metal atom and its surrounding coordination elements. Therefore, engineering the coordination environment near single metal sites, from the first coordination shell to the second shell or higher, would be a rational way to design efficient SACs with optimized electronic structure for catalytic applications. The wide range of coordination configurations, guaranteed by the multiple choices of the type and heterogeneity of the coordination element (N, O, P, S, etc.), further offer a large opportunity to rationally design SACs for satisfactory activities and investigate the structure–performance relationship. In this review, the coordination engineering of SACs by varying the type of coordination element was elaborated and the photocatalytic water splitting of SACs was highlighted. Finally, challenging issues related to the coordination engineering of SACs and their photocatalytic applications were discussed to call for more efforts devoted to the further development of single-atom catalysis.