The increasing demand for high performance portable electronic devices has promoted the research of flexible energy storage devices, and various devices have been suggested and investigated. Among them, wearable fiber supercapacitors have attracted great attention. However, their performances such as energy density and cycling stability still need further improvement for commercial application. Herein, we have proposed a design of fiber electrodes, in which the acidified carbon fibers were decorated by a reduced graphene oxide (rGO)/g-C₃N₄ coating layer via a facile hydrothermal method. The structural and electrochemical properties of composite fibers were investigated. Finally, parallel and symmetric all-solid-state wire-shaped supercapacitors based on rGO/g-C₃N₄/carbon fibers were fabricated. A specific area capacitance of 61 mF cm⁻² was achieved and 90% capacitance was maintained after 5000 cycles, indicating the excellent performance of the fabricated devices. Such design holds great promise for flexible electronics.