The invention provides a capacitor type ring network cable partial discharge sensor which mainly comprises: a titanium alloy made flat plate which wraps and coats the protection sheath of a ring network cable, and together with the steel armor inside the ring network cable, forms a flat plate capacitor and couples high frequency signals generated by cable partial discharge; an insulation plate which is connected to the titanium alloy made flat plate and wraps and coats the titanium alloy made flat plate so as to resist interference of exterior environment to the coupled high frequency signals; a high frequency wave filter circuit mounted to filter unnecessary waves; a metal box mounted on the high frequency wave filter circuit to prevent water and dust corrosion so that the circuit is not ruined by exterior environment and a TNC joint used to receive partial discharge high frequency signals after the wave filtering process. The capacitor type ring network cable partial discharge sensor is provided with a flat plate capacitor formed from a titanium alloy made square plate wrapping and coating the protection sheath of the ring network cable and the steel armor inside the ring network cable to couple high frequency signals generated in the partial discharge of the cable. The insulation plate separates exterior interference on the high frequency signals. The wave filter circuit in the metal box filters clutters and the TNC joint draws high frequency signals out of the metal box.