We report a simple fabrication, great performance and cost-effective triboelectric nanogenerator (TENG), which is based on the cycled contact-separation between a polydimethylsiloxane (PDMS) film and a polyethylene terephthalate (PET) film, for effectively harvesting footfall energy. The elastic sponge is first used as the spacer in the TENG, where the size and the thickness of the spacers have a significant effect on the output performance of the TENG. By using the optimized device, a TENG-based shoe insole is used to harvest human walking energy, where the maximum output voltage and current density reached up to 220V and 40µA, respectively. We also demonstrate that the fabricated shoe insole using a single layer of TENG can be directly used to light up 30 white light-emitting diodes (LEDs) in serial connection. By taking the merits of this simple fabrication, outstanding performance, robust characteristic and low-cost technology, we believe that TENG can open up great opportunities not only for powering small electronics, but also can contribute to large-scale energy harvesting through engineering design.