The invention provides a preparation method of a fluorescent carbon quantum dot. The method comprises the following steps: a, taking sorbose as a carbon source, adding the sorbose into a mixed solution of ethanol and water, and fully carrying out mixing, wherein the ratio of the sorbose to the mixed solution of ethanol and water is (0.5-4g):50mL, and the volume ratio of the ethanol to the water is1:(1-3); b, putting the mixed liquor obtained in the step a into a reaction kettle, carrying out a hydrothermal reaction for 2-8 hours at a temperature of 170-200 DEG C, carrying out cooling to roomtemperature after the reaction is finished to obtain a reaction liquid; c, filtering the reaction liquid, and placing the filtered reaction liquid in a dialysis bag for dialysis for 1-3 days to obtaina water solution of the target carbon quantum dot; and d, carrying out vacuum drying on the water solution of the carbon quantum dot to obtain the target carbon quantum dot. According to the preparation method, the sorbose is taken as a carbon source, so that the preparation method has the advantages of simple synthesis process, easy control of conditions and the like, and the prepared carbon quantum dot has good fluorescence stability and wide adjustable range of light-emitting wavelength.