A soil foundation composed of silt and silty clay needs to be improved in order to get its bearing capacity of composite foundation reaching 180 kPa. A series of in-situ improvement tests on the foundation were carried out by the methods of dry jet mixing piles (DJMP) combined with quicklime piles and DJMP. The results of the tests indicate that it is cheaper and more efficient by the method of DJMP combined with quicklime piles than the method of DJMP and that the composite foundation is to attain higher bearing capacity by process of DJMP carried out before quicklime pile improvement than DJMP carried out after quicklime pile inprovement. The calculation methods of bearing capacity for composite foundation of DJMP combined with quicklime pile are proposed.