Abstract: Considering the edge effect, the internal electric field area and the external electric field area of non -parallel plate capacitor are transformed to complex plane of the upper and lower half plane with conformal map- ping. Then we transform them to the upper and lower half plane of the rectangular area of the complex plane. So that it can be used ideal plate capacitor of capacitance calculation formula to calculate the original plate capacitor of ca- pacitance.

Key words: edge effects, conformal mapping, elliptic integral