The inherent surface film resulted from the manufacturing process on the as received B30 Cu-Ni alloy may affect its corrosion behavior, especially the initial stage of corrosion, but there is a lack of methods to quickly evaluate such influence. In this paper, the initial corrosion behavior in seawater of two B30 Cu-Ni alloys of more or less the same chemical composition but with different inherent films resulted by different manufacturing process were studied via immersion test with EIS and Mott-Schottky measurement, as well as SEM and XPS etc. The results show that the presence of Ni oxide and carbon film in the inherent film leads to a higher initial corrosion potential and higher impedance of B30 Cu-Ni alloy with the inherent film rather than that has the film removed, which is not conducive to the rapid formation of a corrosion products film on B30 Cu-Ni alloy in seawater. In particular, when elemental carbon exists in the inherent film, the potential difference between the surface film and the substrate can be maintained for a long time, thus a "large cathode and small anode" will be formed between the surface film and the substrate. This condition leads to localized corrosion of the substrate, significantly reducing the corrosion resistance of B30 Cu-Ni alloy. When the free corrosion potential of the B30 Cu-Ni alloy withinherent film is negative or can be reduced within 1 h and maintained below -0.1 V during corrosion process, a passive film with good corrosion resistance may form on the B30 Cu-Ni alloy surface. When the free corrosion potential of the B30 Cu-Ni alloy with inherent film is positive and maintained for a long time, pitting is easy to occur, which is not conducive to the corrosion resistance of B30 Cu-Ni alloy. It follows that the characteristics of free corrosion potential and its evolution of B30 Cu-Ni alloy with inherent films can be used as an index to evaluate the influence of the inherent films on the corrosion resistance of B30 Cu-Ni alloy.