| Based on theories of finite and infinite element, taking pojia arch-dam as project background, the paper reseach the influence of foundation-dam system to dynamic property and earthquake response, and prove again that simulating the infinite foundation the coupling system of finite-infinite element is superior.In order to be convenient for comparing the author adhibits two kinds of foundation: rigid foundation and elastic foundation. For the rigid model and elastic finite element model the author recurs to ANSYS to analyse its dynamic property and earthquake response. While as to the elastic finite-infinite element coupling model, in order to obtain the result author organizes huge dynamic programs(Through Fortran program Stiff matrix and Mass matrix of element are organized and through MATLAB program dynamic property and Newmark dynamic displacement are obtained), and uses mapping infinite element which can reflect dispacem-ents property of diminishing in semi-infinite materials. Compared and analysed the results of computation, the conclusion is reached:1. Compared with the calculations of dam in rigid foundation, in elastic foundation frequencies are more convergent, and the list of mode shapes are more reasonable, and the displacement of top dam is larger in reason.2. The finite-infinite coupling system used in the paper can not only simulate the infinite foundation perfectly, reflect the scattering phenomenon of waves, but also lessen the cost of calculation. It has significant advantage comparedwith pure finite element method.3. The paper uses two kinds of coupling model to simulate the infinite foundation, and those are 8-node finite element coupling 8-node infinite element and 20-node coupling 12-node infinite element. Compared the results of computation it is known that the latter is more practical and in the course of application it is strongly recommended.
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