Abstract: The measured results of settlement depth for foundations with different breadth,soil deformation area around pile and foundation,interaction coefficient of double pile and load distribution on pile top beneath cap illustrate that the effects of interaction of soil-soil, pile-soil and pile-pile are obviously lower than elastic theory values. It is the fundamental reason why the calculated values of settlement and interaction effect, according to elastic theory,are larger than those measured.The modified calculation models for interaction of soil-soil, pile-soil and pile-pile,are proposed and used in the calculation method for soil-foundation-superstructure interaction of tall building. This paper presents the balance settlement optimum design method based on variable rigidity, which has been applied in 7 projects with excellent results obtained.