Abstract: As the core part of the important infrastructure of water conservancy and hydropower projects, the stability of dam foundation under earthquake is widely concerned. In order to solve the problem of the dynamic response and liquefaction law of saturated sand foundation under dam, two groups of centrifugal shaking table tests are carried out to analyze the influences of overlying loads on the seismic response of this foundation. The test results show that when there are no overlying loads on the foundation, the soil in the lower layer is softened during the vibration, while the soil in the upper layer is liquefied during the vibration, and the acceleration magnification factor of the foundation and the excess pore pressure ratio of the soil first decrease and then increase along the depth direction. When the foundation has overlying loads, liquefaction occurs in the soil at the edge of the overlying loads, and the acceleration magnification factor of the foundation increases gradually along the depth direction and the ratio of excess pore water pressure decreases gradually along the depth direction. The existence of overlying loads of dam can increase the effective stress of soil and reduce the excess pore pressure ratio. After the dissipation of excess pore pressure, the compactness and stiffness of soil is improved. Finally, based on the nonlinear finite element software GEODYNA, the numerical simulation of the two centrifuge tests is carried out, and the results are in good agreement. The results of the tests and the numerical simulation provide the basis for the design and reinforcement of the saturated sand dam foundation.