Electrocatalytic CO₂ reduction reaction (CO₂RR) is considered an efficient way to convert CO₂ into high-value-added chemicals, and thus is of significant social and economic value. Metal single-atomic site catalysts (SASCs) generally have excellent selectivity because of their 100% atomic utilization and uniform structure of active sites, and thus promise a broad range of applications. However, SASCs still face challenges such as low intrinsic activity and low density of active sites. Precise regulation of the microstructures of SASCs is an effective method to improve their CO₂RR performance and to obtain deep reduction products. In this article, we systematically summarize the current research status of SASCs developed for highly efficient catalysis of CO₂RR, discuss the various structural regulation methods for enhanced activity and selectivity of SASCs for CO₂RR, and review the application of in-situ characterization technologies in the SASC-catalyzed CO₂RR. We then discuss the problems yet to be solved in this area, and propose the future directions of the research on the design and application of SASCs for CO₂RR.