Abstract: A piled raft foundation with different lengths and diameters of piles was studied.On the basis of the interaction principle,a method to analyze the piled raft foundation with different lengths and diameters of piles in the layered ground was established.The element-free method was applied to the computation of the raft;and the approximate analytical model of pile-to-pile interaction was used to analyze the pile-soil system of the foundation.The purpose was to solve the computation problem of the piled raft foundation with special pile group where the stiffness of pile and soil was optimized to reduce the differential settlement by changing the pile length and diameter.In addition,the analysis of the piled raft foundation with irregular shape of raft and the optimization of pile-layout could be easily carried out.It was shown by a practical example that the calculated results were identical well to the results of the large-scale model test,so the method is rational and feasible.