The invention discloses a method for preparing nitrogen and sulfur-doped fluorescent carbon quantum dots. According to the method, citric acid is taken as a carbon source, L-glutathione is taken as a nitrogen-sulfur dopant, a microwave oven is taken as a reaction platform, the carbon quantum dots with fluorescence properties are prepared in a heating manner, the residues and moisture are removed through dialysis and freeze drying, and quantum dot powder is obtained. The nitrogen and sulfur-doped carbon quantum dots are prepared by adopting the method disclosed by the invention; the method is simple in operation, low in cost, high in yield, simple in preparation process and equipment, free of a solvent, and easy to popularize and produce on a large scale, and can be rapidly finished within a short period of time; and the prepared carbon quantum dots have the advantages of good water solubility, high fluorescence properties, photobleaching resistance, adjustable emission spectrum, good biocompatibility, low cytotoxicity and the like, and have a good application prospect in the fields of bioimaging, biosensors and photo-electric devices.