Design, construction and operation of earth hydrotechnical structures located in seismic regions require a continuous improvement of computational methods for calculating various loads (static and dynamic ones). On the basis of the developed methodology and the complex of applied programs, an earth dam (Tupolang HPP) is calculated for the basic loads (gravity forces, hydrostatics) taking into account the design features and the actual physical and mechanical characteristics of soil both at the structure and at its earth foundation ( the height of the structure is 165m).The problem is solved in a plane elastic statement by the numerical finite element method. As the result of the calculation the isolines were obtained of equal displacements (horizontal and vertical), stresses (normal, tangential, principal) over the area occupied by the structure and its inhomogeneous foundation. A number of physical conclusions were made regarding the construction of important structures on an inhomogeneous earth foundation.