Degradation of NO3- into harmless N-2 is a significant challenge in the field of water treatment. In this work, 3D self-supported hierarchical electrode composed of ultra-thin Cu nanosheets-assembled micro-columns on porous nickel foam (Cu NSs/NF) was prepared by three steps, including electrodeposition of CuCl-Cu, thermal oxidation into CuCl-CuO and electrochemical reduction into Cu NSs. Benefitting from the advantages of large surface area and highly active interface as well as fast electron-transfer path, Cu NSs/NF exhibits the significant positive-shift of potential and higher current density than other Cu-based electrodes in the electrochemical reduction of NO3 (NO3--ER). Not only that, an extremely high sensitivity of nitrate reduction response up to 11.23 mA mM(-1) cm(-2) was obtained by chronoamperometric test, which is much higher than those of previously reported works. Moreover, a conversion percentage of 99.7% for NO3--ER was achieved on Cu NSs/NF cathode in NO3--ER experiments. Finally, through the cathodic reduction of NO(3)(-)coupled with the anodic oxidation of Cl-, and the subsequent chemical reaction of NH4+ and ClO-, the highly efficient degradation of NO3- into N-2 with selectivity as high as 97.2% was realized. This work provides a highly efficient Cu NSs/NF electrode and a promising way for degradation of NO3- into N-2.