A computer program based on boundary element method (BEM) has been developed to solve three-dimensional Laplace equation. The program is capable of handling both bounded and open bounded problems and featured in a new integration scheme to increase numerical accuracy. Applications have been made to various hydrodynamic phenomena in BWR pressure suppression system. These are three-dimensional pressure distribution on pool boundary and frequency of an oscillating bubble in a limited pool respectively. Numerical results have been confirmed to agree well with either experiment or theory. In the course of applications, the present program proved to be an efficient tool particularly for a class of problems where boundary integral form is possible in mathematical formulation. Computation time required in BEM has been 1/7 of that in FEM for a typical problem.