A novel cotton/Ni/Co-Ni layered double hydroxide (CT/Ni/Co-Ni LDH) hybrid yarn electrode material is prepared by constructing a three-dimensional (3D) metallic Ni conductive network on the cotton fiber surface for rapid electron transportation and subsequently in situ growing Co-Ni LDH nanosheet array layers with high electroactive surface area for faradic reactions. The 3D porous electrode structure facilitates the effective electrolyte ion diffusion. The obtained yarn electrode material shows a high areal capacitance of 1.26 F/cm2 (121571.1 C/cm2) at a scan rate of 5 mV/s, as well as a stable electrochemical performance under various mechanical deformations. An all-solid-state yarn supercapacitor device is further assembled based on the obtained yarn electrode materials, which exhibits a high energy density of 9.3 μWh/cm2 at a power density of 43.99 μW/cm2.