The deep soft foundation（fak≤100 kPa）of storage tanks and other buildings requires large bearing capacity and limited differential settlement deformation,the spacing of piles may be too little or the length may be too long if the single CFG pile is used in foundation treatment.Therefore,the combined composite foundations are needed,the combined composite foundation with the vibro-replacement stone columns is one of them.According to the strengthening mechanism of the combined composite foundation with the vibro-replacement stone columns and the CFG piles,the stress characteristics and the action of CFG pile and stone columns and CFG piles are analyzed.The results show that CFG pile can improve the foundation bearing capacity and reduce the settlement.Based on optimization theory,the optimization design method is established for the combined composite foundation.Finally,the optimization design method of the combined composite foundation is discussed by an engineering case,which shows that the bearing capacity,settlement and economical efficiency meet the engineering requirements.