The invention provides a power supply system of a low-power consumption online monitoring device combing a highly-efficient supercapacitor. The power supply system comprises an electric energy providing unit, an electric energy conversion device and an electric energy storing device, which are successively electrically connected with each other. The electric energy providing unit is tightly attached to the outer wall of an electric power device. The electric energy storing device is electrically connected with the low-power consumption online monitoring device. The electric power providing unit comprises a metal plate and polycrystalline piezoelectric material plates respectively fixed on two faces of the metal plate. One of the polycrystalline piezoelectric material plates is closely attached to the outer wall of the electric power device. The electric energy storing device is a flat plate-shaped supercapacitor. According to the invention, the power supply system is advantageous in that the power supply system is simple in structure, free from electromagnetic interference, pollution-free and easy to process and microminiaturization of the power supply system is easy to achieve; a stable, reliable and effective power supply source is provided for the low-power consumption online monitoring device; and reliable operation of the low-power consumption online monitoring device on the electric power device is ensured.