Abstract: Based on two groups of four-pile field tests on a multi-type-pile composite foundation, the pile-soil stress, load sharing mechanism and its development character of the multi-type-pile composite foundation are analyzed. Based on the test results of horizontal displacement of deep soils in multi-type-pile stress and loading process, the theory of stress diffusion angle of the multi-type-pile composite foundation is discussed. The problems of stress compound method in calculating parameters for the bearing capacity of composite foundations are discussed. This work will contribute to the theoretical and technical development of the composite foundation. Moreover, to solve these problems needs effective tests and filed measurements in the future.