Caisson-pile composite foundation has unique advantages in deep-water bridge engineering. In order to further reveal the bearing capacity of this foundation under horizontal loads, models of various caissons and piles were designed and tested in sand under horizontal load and the results were compared with the current code. Tests results show that the horizontal bearing capacity of the caisson-pile composite foundation is much higher than single caisson or pile, and load-displacement curve reveals nonlinear characteristics. Caisson-pile composite foundation mainly relies on the earth pressure of passive zone of side wall and bottom friction resistance of caisson to resist horizontal load during the initial period. With the load increasing, the role of pile groups begin to play, and the final proportion of sharing load is nearly 1/3 in the test. Modified GEP method can provide more accurate calculation results. The above good performance of caisson-pile composite foundation makes it possible for its applications in complex environments.