Abstract: Deep mixing cement pile is a effective method to reinforce thick soft clay ground.In allusion to the typical thick soft clay in Wenzhou,this paper analyses the chronically monitored settlement of 4～8 floor building’s composite foundation reinforced by deep mixing cement piles,and calculates the settlement with traditional method,and find that calculated settlement is 2 times greater than monitored value.The structure characteristics typical soft clay is studied through experimentation,and the yield stress ratio of soil structure is found in the range of 1.7～2.5,and the settlement of building will be effectively controlled when the sum of superimposed stress and effective self weight stress is less than yield stress of soil structure in under lying soft layer.Finally, referring to other researchers’ studies and in view of the influence of soil structure characteristics to the settlement of under lying soft layer, a new settlement calculation method has been put forward.With this method,settlement of 12 buildings are calculated and the calculated results are very close to the monitored results.