A triboelectric nanogenerator (TENG) is a simple and cost effective device that converts ambient mechanical energy into electricity based on the surface contact electrification of thin films. The limited surface charge density may affect the overall performance of the TENG. In this paper, a novel electret film based TENG (E-TENG) fabricated by corona charging is proposed that greatly enhances the effective surface charge density of the thin films as compared to those subjected to contact electrification. The short-circuit current, transferred electric charge density, and open-circuit voltage of the E-TENG have been investigated, using different corona charging voltages, pinpoint distances and times in order to explore the optimum experimental conditions. The short-circuit current, transferred electric charge density, and open-circuit voltage of the E-TENG are found to be about seven times larger than those of the ordinary polytetrafluoroethylene (PTFE) film based TENG. Based on corona charging, several multilayered E-TENGs have been fabricated, and the short-circuit current, transferred electric charge density, and open-circuit voltage of the E-TENGs with different number of layers are studied for achieving optimal performances. This work offers an effective approach for improving the effective surface charge density and thereby increasing the output capability of the TENG, which would greatly promote TENG applications in self-powered portable electronics and sensor networks.