Recently, the topic of developing lightweight, flexible and implantable energy storage systems to address the energy-supply problem of wearable electronics has aroused increasing interests. In this paper, by introducing reduced graphene oxide (rGO), we successfully converted the commercial cotton fabric into free-standing, electrically conductive and electrochemically active fabric. Flexible supercapacitor based on the obtained conductive reduced graphene oxide-carbonized cotton fabric (rGO/CCF) exhibits high capacitance (87.53 mF cm−2 at 2 mV s−1), well cycling stability (89.82% capacitance retention after 1000 charge–discharge cycles) and excellent electrochemical stability (90.5% capacitance retention after 100 bending cycles). Moreover, a macroscopic three-dimensional sandwich-interdigital device structure was designed to enhance the supercapacitor performance. The unique rGO/CCF based sandwich-interdigital structure (SIS) supercapacitor shows a volumetric capacitance of 5.53 F cm−3 at current density of 0.0625 A cm−3 in aqueous electrolyte, which is 1.67 and 4.28 orders higher than the traditional sandwich structure (SS) and interdigital structure (IS) supercapacitor based on the same electrode material and electrolyte. Furthermore, energy density enhancement of the supercapacitor has also been achieved by adopting the well-designed device structure. The original SIS supercapacitor based on the elaborate device structure and high-performance electrode material may provide new design opportunities for flexible energy storage devices.