Copper nickel alloys have excellent corrosion resistance and mechanical properties, therefore it is widely used in marine engineering. However, due to its complex service environment, copper nickel alloys are prone to corrosion and leakage, resulting in irreversible losses. A corrosion?resistant conversion film was prepared on the surface of copper nickel alloy to improve its corrosion resistance performance; Electrochemical impedance, Tafel polarization curve, scanning electron microscopy, and energy spectrum analysis were performed, and the surface covered corrosion products of the conversion film were observed by X?ray photoelectron spectroscopy (XPS). The results showed that when the B10 copper nickel alloy sample was immersed in a solution containing molybdate for 120 minutes, the solution transfer resistance (R_ct) and membrane resistance (R_p) reached their peak values, and the corrosion inhibition rate was as high as 92.5%; the conversion film contains copper and nickel oxides as well as hydroxides, while molybdenum exists in the form of +4 and +6 valence oxides.