Abstract: This study has conducted numerical simulations using a three-dimensional finite element method and an analysis on the deformation coordination of core-wall and the transition layers on its both sides for an earth dam with a homogeneous asphalt concrete core-wall in Yunnan province, focusing on core-wall anti-seepage effect and its trend of variation with core-wall thickness. A constitutive model for simulations of the dam body and core-wall was based on the Duncan E-B model. For the cases of different core-wall thicknesses, simulation data were analyzed and the deformation coordination and core-wall anti-seepage effects were compared. Results show that with core-wall thicknesses of 0.3, 0.4 and 0.5 m, most of the horizontal displacements can be well coordinated, but the stream-wise horizontal displacement is increased with an increasing core-wall thickness, resulting in an obvious arch effect in late stage, which is an adverse condition to horizontal deformation. As for vertical deformation, the subsidence of core-wall and transition layers becomes larger as elevation increases, and an increase in core-wall thickness will reduce the peak subsidence. Relative to the transition layers, subsidence of the upper core-wall is smaller while the lower part greater, so that a phenomenon that the whole core-wall has been "stretched" vertically can be observed. This provides a favorable condition to enhance the core-wall arching effect. Since the core-wall is dominated by compressive stress according to the calculations, hydraulic fracturing damage will be impossible. For a dam body imbedded with an asphalt concrete core-wall, its saturated surfaces are lowered significantly and its anti-seepage effects become better; the seepage flow decreases with an increasing core-wall thickness.