Unlike the conventional Newmark slope model (CNM), a potentially sliding soil block may undergo small displacement immediately before sliding in a thin layer underneath. Hence, a Spring-Supported Newmark model (SSNM) has been developed by adding a linear spring for the pre-sliding yield displacement u₀ to a slider of the CNM, which has demonstrated a good reproduction of slope sliding in a model test. Dynamic responses of typical slopes to harmonic and earthquake motions have been calculated incorporating the yield displacement u₀ of only a few millimeters to find out that the acceleration for slide initiation tends to overshoot the yield acceleration of the CNM by a larger margin. Accordingly, the slope displacement tends to decrease by more than a half, demonstrating a great impact of the SSNM considering a small yield deformation u₀ as a specific input parameter.