The role of water molecules on the adhesion property of cellulose/phenolic adhesive interface is investigated by molecular dynamics simulations. Cellulose is one of the most abundant substances in the world, and the major constituent in the wood structure. Phenolic adhesive is largely used in the wood manufacture for gluing the wood panels together. The cellulose/phenolic adhesive interface is a representative of the interface between the wood panels and adhesives in the wood products. As the wood panels and adhesive are sensitive to environmental humidity, the interfacial adhesion of such interface when subjected to a humid environment can be a major factor in the durability of final products. Here, the simulation results reveal that water molecules significantly reduce the adhesion energy between cellulose and phenolic adhesive of 86.5%. Meanwhile, it is demonstrated that the adhesion energy can be recovered after the interface experiences further dry conditioning. The hydrogen bonds between the cellulose and phenolic adhesive are found to account for the strong interfacial adhesion, which can be interrupted in the presence of water molecules and recovered after further dry conditioning. The durability of the wood products is mainly determined by water molecules absorbed at the bilayer interface, which should be considered in a wet condition.