In recent years, there has been significant progress in the field of perovskite research. One area that has garnered attention is lead-free perovskite due to its stability, lack of toxicity, and exceptional optical properties. In this study, we successfully synthesized environmentally friendly, small-sized double-layer perovskites Cs4CuSb2Cl12 using a top-down method involving ball milling. The resulting Cs4CuSb2Cl12 nanoparticles exhibit high photocatalytic capacity, with a 1.60-fold increase in CO yield under full spectrum irradiation for 4 h, from 45.01 μmol/g to 72.17 μmol/g compared to the original material. Additionally, CO evolution under NIR light illumination for 4 h increased from 2.31 μmol/g to 5.37 μmol/g. The top-down treatment resulted in smaller particle size and larger specific surface area, shortened carrier transmission distance, and enhanced electron concentration. Furthermore, the material’s surface presented a high concentration of defects, displayed high absorption capability across the entire spectrum, and abundant photocatalytic active sites. This study introduces an effective and environmentally-friendly strategy to enhance the photocatalytic efficiency of Cs4CuSb2Cl12, providing a new perspective for providing the photocatalytic capability of these materials.