Abstract: In order to study the effect of earthquake on the liquefiable soil layer of saturated sandy soil foundation of earth-rock dam of a reservoir, taking earth-rock dam of a reservoir as the background, FLAC3D is used to analyze the liquefaction distribution law, the deformation characteristics of dam body and the stability of dam slope under the Practical Two-surface Plastic Sand (P2PSand) constitutive model and Finn constitutive model. The results show that the liquefaction degree and range of the silty sand layer under P2PSand model and the displacement of the dam body of the reservoir are greater than Finn model, and the horizontal displacement is more significant. Under the two constitutive models, two obvious sliding surfaces appear in the dam body of the reservoir, and the stability decreases.