Excavation in water area is located at the junction of land and water or directly in the water area,which suffers the impact of wave and tide,so the design method of excavation in water area is different from that of excavation in land.Based on the excavation of water intake of a project in Macao,the paper studies the deformation and internal force of the enclosure wall by using elastic foundation beam theory and numerical simulation when the excavation suffers hydrodynamic load and no hydrodynamic load respectively,and analyzes the sensibility on the rigidity of the enclosure wall and the parameter of pit bottom reinforcement.The results show that using enclosure wall of high rigidity in the water side and pit bottom reinforcement can reduce the deformation and enhance stability of the excavation obviously.The research can provide design ideas and methods for similar projects.