Preparation method of nano-porous carbon material

The invention provides a preparation method of a nano-porous carbon material. The preparation method comprises the following steps: step (A) mixing alkaline waste liquid with water, and performing freeze-drying to obtain a solid mixture, wherein the alkaline waste liquid is produced in the chemical de-ashing process of coal; step (B) carrying out medium temperature treatment on the solid mixture to obtain a pretreated product; and step (C) carrying out high temperature activation on the pretreated product to obtain the nano-porous carbon material. According to the preparation method, the alkaline waste liquid produced in the chemical de-ashing process of coal is used as a raw material, alkali and a small amount of metal ions in the waste liquid are used as an activator and a pore-forming agent of the activation process, and finally the obtained nano-porous carbon material has a large specific surface area, can be used as an electrode material to be applied to supercapacitors and exhibits a high electrochemica