The invention relates to the technical field of carbon material preparation, and particularly discloses a eutectic solvent, application thereof, a carbon quantum dot and a preparation method of the carbon quantum dot, wherein the eutectic solvent is prepared from a nitroimidazole compound and an alcohol compound in a molar ratio of 1: (7-9). The preparation method of the carbon quantum dot comprises the step of reacting the eutectic solvent with a cellulose nanocrystal to obtain the carbon quantum dot. The diameter distribution of the prepared carbon quantum dots is 1-5nm; the fluorescence quantum yield is 20 to 25%; the prepared carbon quantum dots have good photoluminescence and high light resistance; the preparation method not only reduces the pollution during the preparation process, but also improves the material utilization rate, and the preparation method provided by the invention has the advantages of simple process, convenient operation, low cost, low toxicity and environmental protection, is a preparation method with low cost, ecological friendliness and resource conservation, and has wide application prospect..