A numerical calculation model of the dynamic response of a tall building -base- foundation system was built. In the modeling, the beams, columns and stakes was described by the BEAM188, and the floor slab described by the SHELL63. The natural frequency and mode of the vibration of the system were calculated by using ANSYS and the response of the system under both horizontal and vertical seismic action were calculated by using the module, Time-History Seismic Analysis, with the elastic modulus of foundation being set as 20MPa, 20GPa, and 30GPa respectively. The result shows that, the horizontal displacement amplitudes of the system were 0.198m, 0.095m and 0.095m respectively under horizontal seismic action, and were 1.13×10-5m, 1.4×10-11m and 1.4×10-11m respectively under vertical seismic action. So the structures on soft foundation take on stronger capacity of resisting vertical earthquake than that on rigid foundation, and the opposite is the case of resisting horizontal earthquake. The story drifts are respectively 6.2×10-12m, 2.34×10-6m and 3.46×10-6m under horizontal seismic action, and respectively 4.3×10-12m, 4.85×10-6m and 4.78×10-6m under vertical seismic action. The story drifts on soft foundation under both horizontal and vertical earthquake action are much less than that on rigid foundation.