Abstract: NiCrMo alloys serve as critical materials for marine engineering, and their corrosion resistance is strongly dependent on the characteristics of the surface passive film. The Ni/Mo ratio (molar ratio)acts as a key factor affecting the passivation behavior of such alloys, while its internal mechanism remains unclear. To solve the above problem, this paper systematically investigated the effect of the Ni/Mo ratio on the corrosion resistance and passivation behavior of NiCrMoAl alloys in a 3.5% NaCl solution at room temperature. Five tapes of Ni_74.8-yCrMo_yAl (y=0.5, 1.8, 3.1, 4.4, 5.7) alloys with different Ni/Mo ratios were prepared via vacuum arc melting. Electrochemical tests, including open-circuit potential measurement, potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky analysis, combined with X-ray photoelectron spectroscopy (XPS) characterization, were performed to explore the corrosion behavior and passive film characteristics of NiCrMoAl alloys under as-cast conditions and after short-time heat treatment at 800 ℃ for 10 min. Results show that all as-cast alloys consist of a single face-centered cubic phase, and no new phases precipitate with the variation of the Ni/Mo ratio. Among the as-cast alloys, Ni_74.3CrMo_0.5Al exhibits the highest charge transfer resistance of 11.89×10⁵ Ω·cm² and the lowest corrosion current density of 0.81×10^-7 A/cm². This phenomenon is attributed to the low defect concentration and the highest Cr₂O₃ content in its passive film, which significantly improve the compactness and ion barrier capability of the passive film and further enhance its protective performance. Notably, the Ni_71.7CrMo_3.1Al alloy can form a passive film with an extremely low defect density under anodic polarization, whereas it presents high electrochemical activity at open-circuit potential, leading to poor overall corrosion resistance. After short-term heat treatment at 800 ℃, a NiO oxide layer forms on the alloy surface. The corrosion current density decreases by one order of magnitude, while the pitting potential drops significantly. The results indicate that heat treatment improves the uniform corrosion resistance of the alloy but increases its pitting corrosion susceptibility, which is mainly caused by the local depletion of Cr and Mo elements on the alloy surface due to oxidation. The research findings provide experimental evidence and theoretical guidance for the development of high-performance NiCrMoAl alloys for marine applications.