Abstract: Considering the characteristics of integral mutual action between pile,soil and cap,the model of long-short-pile composite foundation was established,and the mechanics of such composite foundation were fully discussed.Based on the shear displacement method,the Mylonakis & Gazetas models for mutual action between two piles and between pile and soil were introduced,and then the flexible factors of mutual actions were provided.Considering the performance of cushion,a method to analyze the settlement of long-short-pile composite foundation was deduced,which could consider the mutual actions between pile,soil and cap,and the correlated program was also developed.Finally,when the method was used to analyze the practical project,its feasibility was proved by the reasonable agreement between the calculated and the measured values.