Copper-nickel alloys are extensively used in precision instruments, ship building, building decorations, and currency manufacturing because of their excellent mechanical properties, good corrosion resistance, and silvery metallic luster. However, they are likely to suffer from discoloration owing to corrosion in the polluted atmosphere containing SO₂. HSO{}_{\mathrm{3}}^{-} and H⁺ exhibit ionization when SO₂ is adsorbed and dissolved in the thin liquid film on the surface of white copper. These sulfide-containing media will accelerate the corrosion process and affect the surface gloss. Benzotriazole (C₆H₅N₃, BTA) is a corrosion inhibitor commonly used in Cu and its alloys that forms a chemical conversion film. It mainly protects the copper-nickel alloys in solutions containing Cl^- or seawater polluted by sulfides. However, some studies have investigated the chemical conversion films of BTA that are affected by atmospheric pollution in the medium, especially focusing on analyzing their failure mode. This experiment was conceptualized based on the aforementioned problem. The corrosion behavior of the copper-nickel alloys protected by BTA in a simulated urban atmospheric environment was analyzed through SEM/EDS, XRD, and electrochemical tests. The laboratory experiments were accelerated by salt deposition. Results showed the presence of prismatic salt crystals on the surface of the copper-nickel alloy treated using BTA during the early stage of corrosion, indicating that the corrosion medium could not completely penetrate the substrate. The corrosion current density of the alloy protected by BTA will decrease first and then increase with the increasing corrosion time. This can be attributed to the oxidation and the presence of BTA chemical conversion films on the surface of the alloy; corrosion was delayed because of the combined action of these two factors. When the BTA film was damaged because of continuous consumption in the local area, the corrosion area expanded, increasing the corrosion current density. Be similar to the samples without BTA treatment, the final corrosion products of the samples treated with BTA were also loose and porous, and the main components were ZnSO₄·6H₂O and Cu₄(SO₄)(OH)₆. However, the degree of corrosion of the alloy protected by BTA was more slight according to the cross-section morphology observation and mass dynamic curve analysis.