The invention provides a method for preparing black light-permeable amorphous niobium pentoxide. The method comprises the following step: pressurizing monoclinic-phase H-Nb2O5 to 21.3-30.0 GPa, thereby obtaining the black light-permeable amorphous niobium pentoxide. By virtue of a high-pressure treatment method, a black amorphous Nb2O5 material with good light permeability is prepared; at normal pressure, Nb2O5 can maintain a stable amorphous structure and good light permeability; the method is simple in operation process and easy to operate.