The structural shape of the interface between ametal and dielectric material in a triboelectric nanogenerator (TENG) is an important factor that can improve the device performance. Many interfacial structures have been developed to improve the TENG performance. However, there have been very few studies on the numerical interpretation of various types of contact interfaces. For various interfacial structures on which uniform triboelectric charge density is distributed, the surface charge density (in-plane, out-of-plane, and total) is systematically analyzed to predict the quantity of the transferred charges on the bottom metal under a short-circuit condition. In this work, a numerical study is conducted using a finite element method. The numerical results confirm that the increase in the quantity of the transferred charges collected on the bottom metal via electrostatic induction is related to the increase in the area of the surface structures (i.e., surface enlargement effect due to the formation of complex interfacial morphology). The estimated magnitude of the transferred charges shows the following decreasing trend for the various structural shapes: rectangle > cylinder > pyramid > cone > flat.