Abstract: Under the conditions of three dimensions, the stability of a bucket is one of the complex stability problems of the interaction between dimensional structures and soil mass. Based on case studies of real works, a finite element model (FEM) for the three-dimensional new bucket foundation breakwater has been established, and the stability of the bucket has also been analyzed. It is found from analyses that the calculation between the dynamic displacement and the static displacement is inconsistent. In regard to this problem, an equivalent quasi-static method has been proposed, which is a method transforming the dynamic problems to the static one. Under the action of the dynamic load, the water pressure will rise and reach a stable value; in another situation, the water pressure will also rise under the action of the static force. If the water pressure is equal for the two situations, then the equivalent static method can be applied to the calculation of the dynamic displacement. The key point of this method is to find the relationship between the bottom pore pressure response of the front end of the bucket and the static load, and the relationship between the bottom pore pressure response of the front end of the bucket and the dynamic load. Based on the two relationships, the relationship between the static load and the dynamic load can be established. From comparison between the numerical simulation results and test results, it is proved that this method is reasonable. On the basis of simulating and analyzing the prototype bucket foundation structure, the relationship is approximatively linear between the bottom pore pressure response of the front end of the bucket and the static load under different model sizes and different heights of the load application points.