The invention provides a carbon quantum dot with a zwitter-ion structure on the surface as well as a preparation method and application of the carbon quantum dot. The preparation method comprises thefollowing specific steps: grinding lecithin into powder and then dispersing the powder into water to obtain a dispersed lecithin solution; transferring the obtained lecithin solution into a hydrothermal reactor, heating the hydrothermal reactor for certain time, naturally cooling and taking out to obtain a brown coarse solution; centrifuging the obtained brown coarse solution and filtering to remove residues, thus obtaining a brown clear solution; carrying out freeze drying on the obtained brown clear solution to obtain the carbon quantum dot. The technical problems that the carbon quantum dotin the prior art has lower stability and cannot realize long-term circulation in a living organism under the condition of different pH values are solved. The preparation method disclosed by the invention is simple and feasible and low in cost; the prepared carbon quantum dot has the advantages of good stability, uniform particle size distribution, good monodispersity and the like; the carbon quantum dot can be applied to nano-carriers of drugs, in particular to antitumor drugs and achieves treatment purpose.