Abstract: Based on the supporting stiffnesses of single pile and soil as well as the equivalent interaction factors of pile-cap in nonhomogeneous soil,a single pile-soil-cap interaction equation was established.A simplified analytical approach was proposed to predict the behaviors of single pile-soil-cap in nonhomogeneous soil.The rationality of the proposed approach was shown by a good agreement between the results computed by the simplified analytical method and those of finite element methods and Butterfield approach.Parametric studies were presented.When the pile slenderness ratio l/d ≥30 and the cap-pile radius ratio n≤4,the percentage of load shared by the cap would be small,and the effect of the cap on the supporting stiffness of single pile-cap system might be negligible.There was obvious effect of the incremental coefficient of elastic modulus with the depth,kE,on the behavior of the single pile-cap foundation,and the relation between supporting stiffness of the single pile-cap system and kE was approximately linear.