Triboelectric nanogenerator collects kinetic energy from human activities and endows sustainable operation of wearable electronics. This work reports a very natural design of triboelectric nanogenerator for harvesting low-frequency walking energy. In the protocol, the human body and ground serve as electrodes of the triboelectric system, which helps the rubber soles to collect mechanical energy during walking motion of humans and produce pulsed alternative currents. The average open-circuit voltage and short-circuit current produced by the system at low frequency are about 400V and 12μA, respectively. Considering the very simple structure, this natural triboelectric nanogenerator can be easily integrated into wearable electronics and take full advantage of human motions as power source and as self-powered systems.