The invention discloses a method for synthesizing nitrogen doped carbon quantum dots based on one-step monocomponent hydro-thermal synthesis, which comprises the following steps: mixing and dissolving ammonium citrate with water, putting the mixture in a sealed reaction vessel, performing heat preservation at 140-220 DEG C for 4-48 hours, after the reaction, naturally cooling to room temperature, and separating the product by a silica gel chromatographic column to obtain the nitrogen doped carbon quantum dots. Compared with existing methods, the method of the invention adopts a single and cheap raw material, is simple in steps, easy to operate, and suitable for mass production.