The subject of this experiment was Hg2+, Hg2+ was detected by L cysteinemodified CdTe quantum dot solution, and Hg2+ was combined with the surfacemodified quantum dots to cause fluorescence quenching of quantum dots, Hg2+ concentration and fluorescence. The intensity of annihilation had a linear relationship. This linear relationship was used to quantitatively detect the Hg2+ content in the solution by quantum dots. The detection band was 400~800nm.The detection limit of the method under optimized conditions was 6.11×10-9mol/L (S/N=3, n=11), and the linear range was 9×10-9~5×10-6mol/L. The deviation (RSD) was 2.86%. In a certain experimental environment, the variable normalization (SNV) preprocessing of the characteristic band and the partial least squares (PLS) modeling analysis can obtain better selfprediction ability and actual prediction ability, and the determination coefficient of the correction set reached 0.8784. The standard deviation was 11.6313μmol/L, the determination coefficient of the validation set was 0.7287, and the standard deviation was 18.7174μmol/L. The results showed that the modeling effect was good, the operation was simple and convenient, the experiment was fast, reliable and nonpolluting, which indicated that the method of detecting Hg2+ by quantum dot fluorescent probe was feasible.