The geological and topographical asymmetries of high arch dam foundations are essential problems which threaten the arch dam safety. Based on Baihetan arch dam engineering, a geomechanical model test is conducted to particularly evaluate the characteristics of the high arch dam with an asymmetrical foundation, from the respects of states of stress and deformation of the dam and its failure modes. Three-dimensional numerical simulations are built on both original and improved design schemes, based on which elastic-plastic finite element analysis is conducted. A comparison is then made between two sets of results in terms of dam deformation, stress distribution in dam abutment, local and global stabilities of the structure. The actual effect and reinforcement mechanism of the design optimization and reinforcement measures, adjusted to those existed asymmetries of dam foundations, are evaluated by combining with experimental results. It is shown that the optimization of dam shape and foundation reinforcement act synergistically to improve the dam deformation, state of stress and transmission of force in dam abutment area, and global stability of the dam-foundation system. The research of Baihetan arch dam asymmetry problem is significant to deepen the comprehension of optimization design and engineering reinforcement especially for high arch dams.