An ammonium perchlorate (AP) composite system with double-coating encapsulation based on the interfacial polymerization behavior of dopamine (DA) in Pickering emulsions was designed to enhance the combustion performance of HTPB-based propellants. The composite system proved highly effective in mitigating the agglomeration issues associated with iron oxide nanoparticles (Fe2O3 NPs) as catalysts, with the AP exhibiting superior performance compared to the composite comprising pure Fe2O3 NPs. The results of the thermal decomposition experiments showed that the HTD temperature of AP@PDA@Fe2O3 was reduced to 318.8 °C, accompanied by a 183.8% increase in heat release and an approximately 30.0% decrease in the activation energy. The combustion rate of AP@PDA@Fe2O3/HTPB was enhanced by approximately 3.0 times higher than that of AP/HTPB. Furthermore, experimental results on safety and surface hydrophobicity showed that the impact sensitivity of the composite AP increased by 28.6%, while the water contact angle was markedly elevated. The reason for the performance enhancement was the synergistic catalytic effect of PDA/Fe2O3 on AP and the dense double-coated structure. This study provided a new idea for the multilevel surface modification of other energy-containing materials.