Recently, single-atom catalysts (SACs) are of great interest in the field of catalysis. Current research shows that it is a potential and feasible development direction for precious metal materials to be made into SACs. Reducing the metal content as much as possible gives the single atom catalyst an obvious cost advantage. However, very low metal loading does not always provide sufficient catalytic activity for SACs. In some catalytic reactions, the deficiency of low catalyst loading can be offset by the increase in catalyst usage. But the excessive use of a catalyst may lead to the loss of mass transport and then the power density. The single atom and high loading might seem like a paradoxical concept but for catalysts, the sufficiently high specific catalytic activity evolves into a most critical parameter for SACs. Synthesizing high loading SACs under control will be an important direction in the next stage of development. In this review, we focus on the progress of precursor selection, material synthesis, content of single-atom, and some possible solutions for high loading SACs. Meanwhile, we also propose a single atom aerogel catalyst with high loading, which provides more possibility for the future development of catalysts.