A method is provided for producing electrodes of flow cell having high power density. A plurality of seeds are distributed on a surface of a conductive carbon material. The seeds are etched into nanoparticles to form carbon nanotube (CNT) electrodes. The present invention can be applied to vanadium redox flow cell with advantages of the CNT electrodes, such as conductivity, corrosion resistance, mechanical strength and specific and electrochemical surface area. Electrons are directly passed to the material through CNTs and then to an external electronic load for improving power density of flow cell, making a cell pack more compact and reducing energy consumption on charging and discharging without using noble metal material.