Flexible supercapacitors have received considerable attention for their potential application in flexible electronics, but usually suffer from relatively low energy density. Developing flexible electrodes with high capacitance and constructing asymmetric supercapacitors with large potential window has been considered as the most effective approach to achieve high energy density. Here, a flexible electrode with nickel cobaltite (NiCo2O4) nanowire arrays on nitrogen (N)-doped carbon nanotube fiber fabric (denoted as CNTFF and NCNTFF, respectively) was designed and fabricated through a facile hydrothermal growth and heat treatment process. The obtained NCNTFF-NiCo2O4 delivered a high capacitance of 2430.5 mF cm-2 at 2 mA cm-2, a good rate capability of 62.1 % capacitance retention even at 100 mA cm-2 and a stable cycling performance of 85.2 % capacitance retention after 10,000 cycles. Moreover, the asymmetric supercapacitor constructed with NCNTFF-NiCo2O4 as positive electrode and activated CNTFF as negative electrode exhibited a combination of high capacitance (883.6 mF cm-2 at 2 mA cm-2), high energy density (241 μW h cm-2) and high power density (80175.1 μW cm-2). This device also had a long cycle life after 10,000 cycles and good mechanical flexibility under bending conditions. Our work provides a new perspective on constructing high-performance flexible supercapacitors for flexible electronics.