The invention discloses a fiber supercapacitor device and a self-monitoring system and method for a charge-discharge state thereof. The device comprises a container and two fiber electrodes, wherein the two fiber electrodes are packaged in the container, metal films with nanoscale thicknesses are plated on outer surfaces of fiber wrapping layers of the two fiber electrodes, electrode active materials are modified on surfaces of the metal films, an inclined fiber grating is engraved in one of the fiber electrodes, micrometer-scale reflecting films are plated on end surfaces of the fiber electrodes, and the container is filled with an electrolyte. The system comprises a light source, a polarizer, a polarization controller, a circulator, a fiber supercapacitor device, a fiber spectrometer andan electrochemical working station, wherein the two fiber electrodes are connected with the electrochemical working station, the fiber spectrometer is connected with the circulator, and the circulator is connected with the fiber electrode engraved with the inclined fiber grating. A traditional substrate material is substituted by fiber, and the miniature and long-distance fiber supercapacitor device having the capability of monitoring the charge-discharge state in real-time and in-situ way is achieved.