Abstract: As a fourth-generation nuclear reactor, the sodium-cooled fast reactor (SFR) is a crucial reactor type for China to realize its closed-cycle nuclear energy strategy. When a sodium-water reaction (SWR) accident occurs in SFR, high-pressure steam enters the sodium loop and reacts with liquid sodium. The two-phase reaction rate model for sodium and water vapor is of great significance for predicting sodium-water accidents and optimizing the treatment of waste sodium. Based on the temperature-dependent liquid film morphology differences observed in previous visual experiments on liquid sodium-water vapor interactions, in this study the Buckingham-Lennard-Jones mixed potential method was employed to investigate the interaction mechanism between molten sodium hydroxide (NaOH) liquid films and water vapor within the temperature range of 600-900 K via molecular dynamics (MD) simulations. Firstly, the applicability of the potential was verified by calculating density and viscosity, then the surface tension was calculated using the stress tensor method, final the intermolecular interactions was analyzed by combining the results of the radial distribution function (RDF) and average molecular coordination number. The results indicate that water molecules form weak hydrogen bonds with hydroxide ions and coordination structures with sodium ions under high-temperature conditions. In the molten sodium hydroxide free surface system, water molecules are mainly distributed on the surface rather than being uniformly distributed due to electrostatic forces. When water molecules are abundant in the environment, they form coordination bonds with sodium ions on the surface of the molten material, gradually converting the electrostatic interactions between ions in the surface layer of the liquid film into water molecule-ion interactions. This process reduces the internal forces within molten sodium hydroxide, thereby decreasing its surface tension. In addition, the diffusion coefficient of water molecules in molten sodium hydroxide was fitted using mean squared displacement (MSD) data at different temperatures. The results indicate that the diffusion coefficient of water vapor in sodium hydroxide increases with rising temperature, which is consistent with the Arrhenius distribution. The calculated diffusion activation energy of water molecules is 31.7 kJ/mol. Compared with the diffusion behavior of water molecules in pure water or aqueous solutions, water molecules in molten sodium hydroxide exhibit a higher diffusion activation energy, indicating that the diffusion process is significantly inhibited. This research provides theoretical support for the study of high-precision liquid sodium-steam two-phase reaction models and holds theoretical significance for the analysis and prevention of sodium-water accidents in sodium-cooled fast reactors.