Objective To develop a colorimetric analysis method for the rapid detection of H₂O₂ in milk.Methods A novel composite nanozyme material, Ag/g-C₃N₄, is synthesized by loading nano-Ag on the surface of g-C₃N₄ nanosheets via a reduction method. The structure and morphology of the material are characterized by X-ray diffraction and transmission electron microscopy. The catalytic conditions for the TMB-H₂O₂ colorimetric reaction are optimized, and catalytic mechanisms and steady-state kinetics are analyzed.Results The Ag/g-C₃N₄ material exhibits good peroxidase-like activity, and the enzyme-catalyzed reaction follows the Michaelis-Menten kinetic model. The optimal detection range for H₂O₂ in the colorimetric system is 10~50 μmol/L, with a detection limit of 0.05 μmol/L. When applied to detect H₂O₂ in real milk samples, the recovery rate is between 99.47% and 102.83%.Conclusion The developed colorimetric analysis method is simple to prepare, cost-effective, highly sensitive, and demonstrates good operability and practicality.