Abstract: Composite photocatalytic materials were synthesized by liquid-phase ultrasonic exfoliation-photochemical deposition method-impregnation method of monolithic Ag, thin layer of graphitic phase carbon nitride (g-C₃N₄) and silica-alumina colloidal spheres (SiO₂). A formaldehyde degradation hermetic chamber was designed to investigate the photocatalytic properties of g-C₃N₄, Ag-g-C₃N₄ and g-C₃N₄-Ag/SiO₂ materials and their degradation effects on formaldehyde. The results show that the efficiency of degradation of formaldehyde can reach up to 65.6% for SAG materials under visible light source conditions. 40% relative humidity can effectively enhance the degradation efficiency.The formaldehyde degradation efficiency decreases by only 9.71% when the silica-alumina spheres load with 30 mg 4%Ag/g-C₃N₄ are recycled for 16 times. The results of material characterization show that the visible light absorption intensity and absorption range of the material are enhanced by ultrasonic stripping and the introduction of Ag, and the separation of photogenerated electrons and holes are effectively promoted, which effectively enhance the degradation efficiency of formaldehyde molecules. The results show that the g-C₃N₄-Ag/SiO₂ material has excellent stability and good photocatalytic performance, which provides a better scientific basis for the application of practical organic pollutant treatment.