In this paper, firstly, the basic principle and efficiency of photocatalytic CO2 reduction are analyzed, and the thermodynamic and kinetic principles of photoreduction of CO2 are explained. Secondly, the graded Cu-NiO composites were prepared using the solution combustion method, and the atomic structure density properties of the graded Cu-NiO composites were calculated using the Hohenberg-Kohn theorem of density generalization theory. Finally, an empirical analysis was conducted to verify the effectiveness of the graded Cu-NiO composites for photocatalytic CO2 reduction. The results showed that the overall capacitance of Cu-NiO composites was between [−3.5*107F−2·cm2,−1.5*107F−2·cm2], and the methanol yield of 4% Cu-NiO composites reached 729 μmol/g cat and the ethanol yield of 4% Cu-NiO composites decreased to 171 μmol/g cat after 5 h of reaction.