Single-atom catalysts with optimal atom utilization and outstanding activity have penetrated the frontier of heterogeneous catalysis. However, the large-scale synthesis of this class of catalysts is still a bottleneck for their industrialization. Herein, we suggest a two-stage micro-dispersion approach to synthesize mesoporous MgAl2O4-supported atomically dispersed Rh, which is more competitive than the batch method for boosting the uniform dispersion of Rh. By increasing the Rh loading, SACs (< 0.05wt%), SACs + NPCs (0.05–0.17 wt%), and NPCs (0.17–1.10 wt%) were obtained and then characterized by the HADDF-STEM technique. For n-octane steam reforming, the TOF of the SAC (0.01 wt%) was approximately 30 times that of the NPC (1.10 wt%), while the Rh amount of SAC was only 3% that of the NPC for the same fuel conversion. Under a high-temperature (750 ℃) steam atmosphere for 15 h, the hydrogen formation rate only declined from 25.1 to 23.8 mol/mol-C8H18.