With the rapid development of wearable electronic and smart electronic devices, the flexible supercapacitors have attracted special attention in energy storage and conversion. Indium selenide (InSe) as a novel two-dimensional layered material has been widely investigated in photodetector, solar cell, and so on due to high electron mobility, anomalous optical response and tuning the bandgap. InSe nanoflakes are obtained from bulk layered InSe materials via a liquid-exfoliation technique and used as electrodes materials of supercapacitors. Flexible all-solid-state supercapacitors (ASSPs) with sandwich structure using InSe nanoflakes have a volumetric capacitance of 3.48 F cm(-3) at a scan rate of 0.005 V s(-1). For improving the performance of ASSPs based on InSe, highly conductive carbon nanotubes (CNTs) are added into InSe nanoflakes to enhance the conductivity of InSe/CNTs composites used as electrodes of ASSPs. InSe/CNTs (mass ratio 6:1) ASSPs deliver high volumetric capacitance of 25.1 F cm(-3) at a scan rate of 0.005 V s(-1), good mechanical properties (93.2% capacitance at 180 degrees bending) and long cycle stability (88.3% capacitance after 10000 cycles). In addition, ASSPs based on InSe/CNTs composites exhibit a high power density of 410.15 W cm(-3) and a superior energy density of 3.48 mWh cm(-3). The InSe/CNTs composite is expected to have a potential candidate in high-performance electrochemical energy storage devices.