To make further research on the horizontal bearing capacity of caisson-pile composite foundation, the model tests on single pile and a series of caisson-pile composite foundations, under horizontal loads and the combination of vertical and horizontal loads in silty clay, are carried out. The relation between load and displacement, bending moments of pile shaft, lateral deflections of pile shaft and efficiency coefficients of group piles are investigated based on the model tests. With the constraint of caisson, the bending moments, displacements and soil resistance of pile shaft under the horizontal loads, can be reduced than the single pile without constraint; the horizontal bearing capacity of composite foundation can be improved. Under the vertical and horizontal combination loads, friction under the caisson bottom and vertical force on the pile top is also conducive to further improve the composite foundation bearing capacity. The efficiency coefficients of caisson-pile composite foundations with different pile numbers, constraint conditions on the pile top and loads on caisson are also obtained. For the case of pile distance is 6 times of the diameter, the mutual influence between each other pile is very small.