Abstract: A new type of prefabricated concrete-filled steel box composite caisson structure was proposed. In order to study mechanical properties of the caisson structure under the water and soil pressure, a full-scale test structure was designed based on the Dayang Parking underground garage project. A static loading test for the structure was conducted to analyze deformation and stress characteristics of the caisson structure under horizontal loads when it was sunk to the design elevation and the baseplate was not sealed, and then the bearing capacity and safety of the caisson structure was evaluated. The results showed that under the 1.1 times horizontal design load, the maximum deformation of the shaft wall for the caisson structure was about 1/1 000 length of the shaft wall, and the stress at each point was less than the yield strength of the material. The caisson structure had great rigidity and the high bearing capacity. The braces and walings of the caisson could effectively improve the stress in the shaft wall and enhance the overall mechanical performances of the caisson structure. The caisson structure was a reasonable structure which could meet the requirements of safety and use.