The manufacture of flexible, miniature, large-area and low-cost energy storge units has attracted much attention with a rapid development of flexible electronic devices. In this paper, NiCo2S4/g-C3N4 nanocomposite material was prepared via a one-step solvothermal process with nickel and cobalt nitrate hexahydrate as raw materials, thiourea as a vulcanizing agent and pyrolysis g-C3N4. The interdigital electrode of NiCo2S4/g-C3N4 was created via mask printing on a polyethylene glycol terephthalate flexible substrate with the well-prepared ink. The flexible interdigital supercapacitor was obtained by coating a layer of gel electrolyte. Based on the structure and electrochemical performance characterizations, NiCo2S4 nanoparticles dispersedly grow on g-C3N4 nanoplates, thus improving the charge transfer and accommodating the volume expansion of NiCo2S4 during charge-discharge cycles. The area specific capacitance of the nanocomposite electrode is 9.1 F/cm2 at a current density of 10 mA/cm2. The assembled supercapacitor can operate at -0.2-0.6 V and remainsstable at a scanning rate of 500 mV/s, revealing a good rate performance. The area specific capacitance of the device is 5.7 mF/cm2 at a scanning rate of 20 mV/s, and the energy density is 0.56 mW?偸h/cm3 at a power density of 17.5 mW/cm3.