NOVELTY - Preparing nitrogen doped graphene comprises (i) preparing graphene dispersion liquid; (ii) mixing the graphene dispersion liquid and nitrogen source, and ultrasonically treating to obtain mixture A; (iii) conveying the mixture A to a pressure microwave oven of 1-50 mPa pressure, placing in a reaction kettle under power of 600-2000 w, and heating for 10-600 seconds to obtain a mixture B; (vi) filtering the mixture B through 0.2 mu m polytetrafluoroethylene filter, and drying the filter cake at 80-150 degrees C for 20-200 minutes.    USE - The nitrogen-doped graphene is useful for preparing lithium-ion battery, lithium-air battery, supercapacitor electrode material, fuel cell oxygen reduction catalyst and other energy materials.    ADVANTAGE - The nitrogen-doped graphene: has high-nitrogen doped content (claimed). The method: consumes low energy; is simple; has convenient operation; and reduces the cost; and provides graphene having excellent electrochemical properties.    DETAILED DESCRIPTION - Preparing nitrogen-doped graphene comprises (i) preparing graphene dispersion liquid having concentration of 1-5 mg/ml, where the dispersoid is double-layer graphene or multi-layered graphene, and dispersing agent is deionized water, anhydrous ethyl alcohol or acetone; (ii) mixing the graphene dispersion liquid and nitrogen source according to mass ratio of 1:0.1-100, ultrasonically treating for 0.5-2 hours to obtain mixture A, where the nitrogen source is polypyrrole, polyaniline, polypyridine, polythiophene, polydopamine, pyrrole, aniline, pyridine, melamine, ethylenediamine, triethylenetetramine, porphyrin, phthalocyanine, phenanthroline, imidazole, thiazole or thiophene; (iii) conveying the mixture A to a pressure microwave oven of 1-50 mPa pressure, placing in a reaction kettle under power of 600-2000 w, and heating for 10-600 seconds to obtain a mixture B; (vi) filtering the mixture B through 0.2 mu m polytetrafluoroethylene filter, and drying the filter cake at 80-150 degrees C for 20-200 minutes to obtain the nitrogen-doped graphene having nitrogen doping amount of 10-15%.