The microbial coral sand pile composite foundation is composed of coral sand and coral sand piles solidified using MICP, which has the advantages of the ability to obtain local materials, less disturbance to the ground and marginal effects to the ecological environment of islands and reefs, and has good application prospects for construction of islands and reefs. Through the model test of single pile composite foundation of biocemented coral sand pile under different working conditions, the influence of relative density (50%, 65%, 72%), area replacement rate (8%, 14%, 20%), water content (dry and saturated) and water level fluctuation on the bearing characteristics was revealed. The test shows that in the dry state, with increase of the relative density and the area replacement rate, the bearing capacity and the pile side friction of the single pile composite foundation of biocemented coral sand pile increase. The axial force of the microbial coral sand pile and the stress ratio of pile and soil decrease with increase of the relative density, and increase with the area replacement rate. The bearing capacity of composite foundation can be effectively improved by increasing the relative density and area replacement rate. The ultimate bearing capacity of the single pile composite foundation of biocemented coral sand pile in the saturated state is 49%-66% of the bearing capacity in the dry state. Under the same upper load and area replacement rate, compared with the dry state, the pile side friction resistance and the maximum pile axial force of the composite foundation in the saturated state decrease, the stress ratio of pile and soil increases. The twice water level rises and falls have marginal effect on the bearing characteristics of single pile composite foundation.