<p>Rockfill dam materials undergo large wetting deformation under the action of water, which leads to uneven settlement of the dam body in the later stage. In this work, on the basis of the discrete element method particle flow code, a triaxial wetting numerical simulation test is carried out to explore the macroscopic mechanical properties of rockfill under wetting and reveal its microscopic deformation and failure mechanism from the macro-mesoscale perspective. The results show the following: (1) The single- and double-line method: according to the test results, there is no significant difference between the single- and double-line methods in terms of the macroscopic stress–strain–volume change and wetting axis-volume change. The particle breakage rate and particle number of the single-line method are greater than those of the double-line method. The corresponding force chain distribution, particle fracture zone position, particle fracture distribution, and displacement field distribution of the single-line method are also more obvious than those of the double-line method, and the wetting path of the single-line method is more in line with the actual situation of the project. (2) Macroscopic law: In numerical tests, wetting deformation increases with increasing stress. The deformation trends observed in the single-line method and the double-line method exhibit similarities. The particle breakage rate associated with the single-line method is 1.48% higher than that of the double-line method, and the increase in particle number is 10% greater compared to the double-line method. Preloading wetting effectively reduces the total deformation of rockfill, and the path of wetting influences the overall deformation to some extent. (3) Microscopic observation: The strong chain density between the particles following wetting exceeds that of the dry particles. A relationship exists between the distribution of particle breakage and the distribution of particle fractures during the wetting process, which shows the occurrence of stress concentration, with the number of cracks in the single-line method significantly exceeding those in the double-line method. The expansion area of the displacement field after wetting is markedly larger than that of the dry sample, and the displacement of particles at both ends of the sample in the single-line method is more pronounced compared to the double-line method. (4) Improving model: the relationship between wetting axial strain and stress level aligns well with an exponential function. The degree of fitting for the linear equation parameters <i>d</i> and <i>f</i>, along with the confining pressure in relation to wetting volumetric strain and wetting stress level, is low. The exponential function relationship is fitted by improving the parameters <i>d</i> and <i>f</i> and the confining pressure, resulting in a higher fitting degree for the improved model curve compared to the original model.</p>