The present invention relates to a preparation method of carbon quantum dots with adjustable fluorescence colors, and belongs to the technical field of nanometer materials. According to method, citric acid or a citrate is adopted as a carbon source, a nitrogen-containing compound is adopted as a nitridation agent, hydrogen peroxide is adopted as an oxidant, a hydrothermal synthesis method is adopted to obtain an aqueous solution of carbon quantum dots emitting blue or green fluorescence under ultraviolet light excitation, reaction conditions are easily controlled, and the method is suitable for scale production. The prepared carbon quantum dots have advantages of adjustable fluorescence color, high yield, high quantum efficiency, good result reproducibility and the like, wherein the product can be directly used for tumor cell labeling and live cell imaging labeling. According to the present invention, only the one reactant is required, the raw materials are easily-available and non-toxic, the production process does not require special protection, the reaction condition is easily controlled, and the obtained carbon quantum dots have advantages of high yield, high quantum efficiency, good result reproducibility and the like; and the method has characteristics of high yield, simple preparation process, low cost, easy scale production and the like.