The parasitic resistance and capacitance can be characterized by the Laplace equation with combined boundary conditions and it can be solved by using the direct Boundary Element Method(BEM).But, it is difficult to treat the discontinuity of normal electric field at corners. The first author of this paper has ever applied a ocncept of multiple normal derivatives at a corner to hadle 2-D problems, and it works efficiently [2,4]. This paper extends the concept to 3-D simulation. Some numerical examples are presented.