A high-performance yarn electrode material, cotton/graphene/polyaniline, is synthesized by coating primary fiber cores inside cotton yarns with graphene sheets and followed by further growing polyaniline nanowire array layers through in situ polymerization of aniline. The electron transportation is enhanced by the 3D graphene conductive network on cotton fibers, which further bridges the polyaniline nanowires. The polyaniline nanowires with small diameters ensure high electrochemically active surface area. The spaces within the polyaniline nanowire array layers and the hierarchical pores of the entire yarn electrode benefit the fast electrolyte ion diffusion. The unique 3D yarn electrode structure results in an excellent electrochemical performance. The maximum areal capacitance and capacitance retention are 246 mF/cm2 at 5 mV/s and 98% after 3800 cycles, respectively. A symmetric all-solid-state yarn supercapacitor is fabricated by using this yarn electrode, which delivers an energy density of 9.7 μWh/cm2 at a power density of 840.9 μW/cm2.