Abstract: In the field of ship hydrodynamics, scholars usually adopt Hess - Smith method to solve the potential flow problem. However, this method is essentially based on the physical intuition, and there are shortcomings concerning this theory in numerical calculation. Since the direct boundary element method is rarely used in ship hydrodynamic problems, the presented method in this paper has broad application prospects in the field of ship hydrodynamics and may promote the direct boundary element method. According to the boundary integral method, an integral equation is established to solve the unbounded potential flow problem, and the flow field velocity distribution on the surface of the velocity potential is then obtained. A comparison with the analytical solution is finally conducted for error analysis. In this paper, both 2D and 3D numerical examples are provided and programmed to realize the numerical calculation process in Matlab. The results show that the direct boundary element method has decent precision and efficiency, and the numerical implementation is even more concise. Moreover, this method can be developed into general forms to solve other ship dynamic problems.