Abstract: Wetting deformation of rockfills affects the safety and stability of rockfill dams, which has always been the focus of engineering and academic circles. However, the mechanism of wetting deformation is still not fully understood at present. The laboratory tests, scanning electron microscope and combined finite-discrete element method are used to study the effects of wetting on the crushing and compression characteristics of the rockfills. The single particle crushing tests and SEM of dry and saturated particles show that the wetting leads to the change of rock mineral composition and microstructure of particles. The pores, microcracks and other defects increase owing to the wetting, which reduce the crushing strength of particles and surface friction coefficient. The mesoscopic parameters of the dry and saturated particles are determined, and the numerical tests on the single particle crushing and the uniaxial compression of the particle assembly in the dry and saturated states are conducted. The wetting has effects of lubricating, softening and degrading on the rockfills, which make the friction coefficient, deformation modulus and crushing strength of the rockfill particles decrease to different degrees. The wetting reduces the crushing strength of the particles by 22.6%, the friction coefficient between the particles by 11.7%, and the compression modulus of the particle assembly by 13.1%. The main reason of wetting deformation of the rockfills is the particle breakage caused by the reduction of crushing strength.