Recently, triboelectric nanogenerator (TENG) has emerged as an important energy harvesting technology and attracted extensive attention. In this work, we report a newly-designed TENG that is composed of a grating-segmented freestanding triboelectric layer and two groups of interdigitated electrodes with the same periodicity. The sliding motion of the grating units across the electrode fingers can be converted into multiple alternating currents through the external load due to the contact electrification and electrostatic induction. With more grating segments being introduced to the structure, the amount of accumulated charges, current density, and output frequency were enhanced substantially, which was demonstrated by both of the theoretical and experimental investigations. Working in non-contact mode, the device showed excellent stability and the total conversion efficiency reached as high as 85% at low operation frequency. On basis of these unique characteristics, the TENG was applied to harvest a variety of biomechanical energy, such as sliding of a human hand and human walking, demonstrating the practicability of using TENG to harness a wide range of ambient motion with high efficiency.