Abstract: In this paper, the relation between cap(foundation) and pile is classified into three types based on the load transfer mechanism.The first one is that pile head is imbedded into cap, the second one is that there is a layer of granular mat between foundation slab and pile head,and the third,as suggested in this paper, is that there is a certain gap between foundation slab and pile head,with the foundation being directly on the top of soil. A series of full scale loading tests are carried out to investigate the difference of the interaction among foundation slab, pile and soil, the failure pattern and the bearing capacity of these different kinds of composite ground under vertical load.