Cushion is the core of composite foundation, which can coordinate the differential deformation between piles and soils. The working characteristics of the cushion may change when the pile penetrated into the cushion, which is lack of inrestigation at present. In this paper, by means of model tests, the working characteristics of the cushion during the penetrating of pile were analyzed by measuring the pile top's pressure, displacement and deformation of cushion. Besides, the effects of the pressure between piles and soil, and the pile diameter on the cushion were analyzed. The results show that, during penetraton process, there are three different deformation stages, i.e., compaction deformation, shear deformation and crush deformation. The pressure between piles and soils affects the whole process of the cushion's deformation, and the bearing capacity and the bearing thickness of the cushion are increased with the pressure. The effect of the pile diameter on the cushion is signigicant in the crushing deformation stage. The bearing thickness of the cushion increased linearly with the pile diameter.