Harvest mechanical energy with variable frequency and amplitude in our environment for building self-powered systems is an effective and practically applicable technology to assure the independently and sustainable operation of mobile electronics and sensor networks without the use of a battery or at least with extended life time. In this study, we demonstrated a novel and simple arch-shaped flexible triboelectric nanogenerator (TENG) that can efficiently harvesting irregular mechanical energy. The mechanism of the TENG was intensively discussed and illustrated. The instantaneous output power of single TENG device can reach as high as∼4.125mW by a finger typing, which is high enough to instantaneously drive 50 commercial blue LEDs connected in series, demonstrating the potential application of the TENG for self-powered systems and mobile electronics.