The demand for portable electronic devices is driving the development of flexible supercapacitor, while current devices still need to improve the performance for practical applications. Here, we report a cost-efficient flexible three-dimensional-Ni (3D-Ni) electrode for a flexible supercapacitor with excellent energy density and power density. The meso-porous 3D-Ni electrode provides a large number of active sites to store charges and good accessibility to the ions in polymer electrolytes, leading to excellent capacitance, high energy density, as well as high power density. The Ni(OH)2/3D-Ni positive electrode showed an outstanding specific capacitance of ~3400F/g at 10A/g and retained 80% of the initial capacitance at 200A/g. The negative MnO2/3D-Ni electrode exhibited a specific capacitance of 1250F/g at 10A/g and excellent capacitance retention of 82% at 200A/g. The Ni(OH)2/3D-Ni//MnO2/3D-Ni hybrid supercapacitor delivered an excellent energy density of 75Wh/kg and a high power density of 5.3kW/kg, and these values did not change under bending conditions. The 3D-Ni electrode introduced here represents a new type of ideal electrode that can be easily applied to various flexible/wearable electronic device with excellent performance.