InSelectromagnetic metrologySandSelectronic instrumentation,Sthe stable capacitance standards including the Selectable Low-value Capacitance Standard(SLCS)are usually required for calibrating the instrumentations and meters. This paper adopts the 3-D electrical field simulation software to research on the edge effect around the hole on the screen shutter which is one of the largest uncertainty sources for the SLCS. On basis of the simulation results the overall mechanical structure for one kind of the SLCS has been designed, which can lay a strong foundation for its actual realization.