Abstract: The conception of stress ratio of composite pile-soil was put forward on the basis of test data of composite foundation of rigid pile with cap to describe its mechanical behavior.Based the on soil mechanics,elastic theory and some reasonable assumptione,adopting the method of the equal settlement section,considering the pemetration of top and fir of pile,the calculation formula of composite foundation with capped rigid pile was proposed,which showed the characteristics of layered soil and its 3D settlement deformation.The spacing and length of pile,size of pile cap,modulus of cushion,modulus of underlying soil layers,modulus of soil besides pile caps and K0 were discussed with practical engineering example.It was shown that the optimized design of the composite foundation with capped rigid pile could be performed with the method.