According to the relationships between the valley shape and the mechanical properties of rock fills, the new valley topography parameters which are described by using a valley width coefficient μ, a valley slope coefficient δ and a valley asymmetry coefficient γ have been given in this paper. And then the new parameters for valley topography are used to study the influences of the valley topography on the deformation and stress characteristics of an asphalt concrete core wall dam. The results of this study show that the valley width coefficients have direct influences on the degree of the arch effect caused by stresses taking place at the bottom of the asphalt concrete core-wall. The smaller the valley width coefficients, the stronger the arch effect caused by the deep narrow valley becomes, and the hydraulic fracturing may be taken under such conditions in practical engineering. When the valley slope coefficients increase, the tensile stress area in the asphalt concrete core wall becomes smaller and the values of tensile stress become larger. The differential settlements on the dam increase obviously with the adding of a valley asymmetry coefficient. A critical value of the asymmetrical valley is proposed according to the differential settlements between left and right sides of the dam. The foundation topography can restrain the deformation of the dam and the valley widths have the most obvious impacts upon the displacement of the asphalt concrete core wall dam.