Abstract: Critical height is a key problem in embankment on soft ground engineering.When embankment height is less than the critical height,settlement and stability of foundations can be controlled.The effect of the reinforced cushion is considered little in the previous theoretical formula.This paper studies the critical height when the reinforced cushion play the role,based on the diffusion theory and the deloading of synthetic materials’ friction drag.At last,the choice of the parameter is discussed.