Based on the characteristic of the grotto rock reinforced by prestress anchor cable, taking three typical engineering sections in Yulin grotto in Anxi county Gansu province, as exampies, the simultating computation for the displacement field and stress field of the grotto rock under seismic load is done using dynamic finite element method, the change regularity and dynamical response of the grotto rock are concluded. Meanwhile through analyzing the characteristic of the frequency spectrum of real seismic load, the influence of sismic load＇s feature period on dynamic response result of the grotto rock is revealed.