Abstract: The stratum in karst area is generally a certain thickness of soft soil overburden,under which there is a thin roof cave with vertical fluctuation and bead shape,which is difficult to be used as a suitable pile foundation bearing stratum.In this study,the finite element software ABAQUS is used to establish the composite foundation model of foam concrete rigid single pile and pile caps.The engineering characteristics of different types of stiff single pile and the engineering properties of different types of stiff composite pile foundation are analyzed,and the deformation characteristics and load transfer rules of the composite foundation are revealed,which provides theory for foundation treatment and reinforcement in the karst area.Based on the analysis,this paper provides a useful reference for engineering designers.