Reinforced concrete has become the preferred choice for modern building structures owing to its long durability, strong structure, flexible, and diverse designs, wide availability, and low cost. Traditional carbon steel bars are prone to corrosion in marine environments, resulting in problems such as steel bar breakage and concrete cracks, thereby affecting the safety and reliability of marine engineering structures. Therefore, using high-performance corrosion-resistant alloy steel bars can effectively solve the problem of steel corrosion in marine engineering and improve the durability and maintainability of engineering structures. Concrete is a highly alkaline environment when it is free from erosion, and the pH value of its pore solution is 12.5-13.6. When steel bars are exposed to this environment, a stable passive film forms on their surface. This spontaneously formed passive film can keep the steel bars in a passive state, preventing corrosion and considerably extending the service life of reinforced concrete structures. The differences in the composition and structure of the passive film on steel bars represent important reasons for the different corrosion resistance performances of steel bars in concrete. To study the passive behavior of corrosion-resistant rebars (20MnSi steel, 3Cr steel, and 9Cr steel) with different Cr contents (0, 3%, and 9%, mass fraction) in simulated high-alkaline concrete pore solution, electrochemical measurements (including open circuit potential, electrochemical impedance spectroscopy, polarization curve, and Mott-Schottky curve) were used to study the changes in the properties of the passive film on the surface of the rebars over time. XPS was used to analyze the composition and structure of the passive film. The results show that a passive layered film was formed on the surface of the rebars in the simulated high-alkaline concrete pore solution, and the structure, composition, and protective properties of the passive film were closely related to the Cr content and passivation time of the rebars. The passive film of 20MnSi steel was mainly composed of Fe(III) compounds in the outer layer and Fe(II) oxides in the inner layer. The outer layer of the passive film of 3Cr steel and 9Cr steel comprised Fe(III) and Cr(III) oxides and hydroxides, and the inner layer comprised Fe(II) oxides and Cr(III) compounds. The passive films formed by the three types of rebars exhibited n-type semiconductor properties within the potential range of -0.8 to 0.2 V (vs SCE). As the immersion time increased, the defect density in the passive film decreased, leading to decreased corrosion current density of the rebars and improved corrosion resistance. When the Cr content is increased, the point defect density of the passive film decreases. At the same time, the passive film becomes dense, resulting in improved corrosion resistance of the rebars.