Fiber supercapacitor (FSC), with the advantages of high power density and ability to be knitted into arbitrary shapes, serves as an ideally energy storage of wearable electronics. Here, we report a high specific capacitance and mechanical strength fiber supercapacitor via synthesizing ruthenium dioxide hydrate (RuO2·xH2O) @graphene in situ on flexible commercial carbon fibers. The typical “cracked mud”-like RuO2·xH2O @graphene uniformly wrap around the surface of the carbon fibers by the vapor-phase hydrothermal method. Meanwhile, Graphene plays a role in linking every two chapped chips of RuO2·xH2O, increasing the electronic conductivity and mechanical strength of the electrode. The fiber electrode exhibits high specific capacitance of 210.14 F cm−3 (0.42F cm−2 and 10.56 mF cm−1). Furthermore, the solid-state symmetric supercapacitor is fabricated with H3PO4/Poly(vinyl alcohol) as electrolyte and displays excellent cycling stability with 98.40% of the initial capacitance after 50000 continuous charging/discharging cycles, as well as good mechanical stability with 96.10% of the initial capacitance after 2000 continuous bending cycles. With merits of flexibility, high specific capacitance and cyclic/mechanical stability, the RuO2·xH2O @graphene carbon fiber enables to knit into any designed shape into energy textiles used as the energy storage module for wearable electronics.