Abstract: Since the wetting deformation of the rockfill material after soaking is not generated instantaneously but rather in a gradual development process, the time-effect analysis for the wetting deformation is proposed in this paper. The formula for the wetting shear strain component of the rockfill material is derived based on the Prandtl-Reuss flow rule. Then the three-dimensional wetting strain component is obtained by superposition of the wetting volumetric strain component. The relationship between the three-dimensional wetting strain component and the wetting strain component in the uniaxial state is analyzed. It is pointed out that the computational formula of the three-dimensional wetting strain component in literature is not rigorous. In analogy with the formula of the three-dimensional rheological deformation of the rockfill material, the time-effect computational formula of the wetting deformation is derived. Example analysis shows that the settlement of the dam crest produced by the wetting deformation increases with time, and the time for the steady deformation is inversely proportional with the rate of the wetting deformation.