We demonstrated a flexible self-powered system that consists of a strain sensor and a nanogenerator. An individual ZnSnO3 microbelt was bonded at its ends to a polyethylene terephthalate (PET) substrate to fabricate a strain sensor and a single-nanobelt nanogenerator. The sensor and nanogenerator were connected in series and packaged by a polydimethylsiloxane (PDMS) layer. The ZnSnO3 belongs to a R3C point group that exhibited a large piezopotential along the z-axis, so that it can be either a power source or a sensor. The piezopotential can drive electrons to flow in the circuit and serve as a power source. The piezopotential can also tune the Schottky barrier height (SBH) at the contact by varying the tensile and compressive strain owing to the piezotronic effect, so that it can serve as a strain sensor. The output current decreased as compressive strain increased, but the current increased as tensile strain increased. The sensor can be switched by bending the flexible substrate, which can act as a highly effective reversible electromechanical switcher.