Abstract: The inertia effect of base soil has so far not been considered in machine foundations and structures design.In this paper the empirical formulas were derived for computing mass of base soil participating in vibration and vertical stiffness of base on the basis of a number of field tests, with linear Mass-damping-spring theory of vibration adopted. Meanwhile, the effect of depth of embedded footings on the mass of base soil participating in vibration is also studied. It shows from a lot of analyses that the accuracy of dynamical computing has been markedly improved, with the inertia effect of base soil taken into account.