Sanwei Mt. active fault is only 3 km from Mogao Grottoes in Dunhuang city, Gansu province. In this paper, based on the horizontal layered & homogeneous seismogenic fault model, the influence of ground motions generated from Sanwei Mt. fault on Mogao Grottoes under scenario earthquakes respectively with magnitude of (5.5,) 6.0 and 6.5 is simulated using the stochastic finite-fault method. It indicates that the distribution of ground motions near Sanwei Mt. fault presents the hanging wall effect of reverse fault. The calculated values of PGA are compared with those deduced from other attenuation formulas based on the data of other areas to validate the calculation result. This study has some reference to aseismatic and reinforced design in Mogao grottoes.