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Water reduces the stability and safety of paving material, and this has been extensively studied in traditional asphalt pavement. However, the influence of water on emerging cold-mixed epoxy asphalt (CEA) has not yet been acknowledged. In addition, the microstructure composed of epoxy resin (ER) and asphalt determines the performance of the CEA binder, and the influence of water entering this structure should be focused on. Here, CEA interfacial water models were established based on experimental and molecular dynamics (MD) simulations. The distribution and motion of the interfacial water and their influence on the energy, compatibility, and mechanical properties of CEA were explored. The results showed that CEA had desirable water stability when the water content was less than 5%. Water moved and was rearranged at the interface of the CEA and tended to move toward the ER. The water diffusion coefficient increased proportionally to the quadratic of the water content, and the structure of the CEA changed from an ordered short-range arrangement to a disordered one. Water reduced the interaction between the ER and asphalt by a maximum of 41.7% but had little effect on the compatibility of the CEA. Water plasticized CEA because the glass transition temperature of the CEA decreased, and less than 3% of water decreased the modulus of the CEA by a maximum of 27.0%. Simultaneously, water also destroyed the isotropy of the properties of the CEA. The gyration radius of the CEA dropped to approximately half of the value without water. This study is positive for promoting the performance improvement of CEA and provides a framework for studying CEA modeling and evaluation with MD simulations. [ABSTRACT FROM AUTHOR]