Mercury ion， a kind of heavy metal contaminant with high toxicity， poses significant health risks to the human body. It is of great significance to control the content of mercury ion in food. Carbon dots (CDs) with high fluorescence were prepared by one-step hydrothermal method， in which citric acid was used as carbon source and different amino acids was used as nitrogen source. The influence of the nitrogen doping of different amino acids on the fluorescence quantum yield (QY) of CDs and the response of these nitrogen doped CDs to mercury ions was explored. The results showed that the carbon chain lengths and functional groups of different amino acids have a certain effect on the QY of CDs. Further， Hg2+ can effectively quench the fluorescence of Gly-CDs doped with glycine as a nitrogen source. Moreover， Gly-CDs has good fluorescence stability. Under the optimal experimental conditions， the linear range of Gly-CDs for the detection of Hg2+ is 0.00-7.00 μmol/L and 8.00-60.00 μmol/L with a detection limit of 0.20 μmol/L. It has been successfully applied to detect Hg2+ in beverage samples. The recovery rate was between 90.08%-107.90%. The method is simple， sensitive， rapid and suitable for accurate determination of Hg2+ in beverages.