The invention discloses a carbon dot component in cola as well as a property characterization method and a practical application method of the carbon dot. The preparation method comprises the following steps: by taking original-taste (1+2) Nestle coffee, pepsi (330ml) and coca-cola (330ml) as main raw materials, separating and purifying through a dextrane gel G-25 column and performing freeze-drying for 24 hours to collect the carbon dot. The coffee/cola carbon dot is relatively low in cost, low in toxicity, simple in extracting method, good in water solubility, good in biocompatibility and can be widely used as a novel fluorescent carbon nano particle in the field of biomarkers.