Abstract: The hydrothermal method for preparation of CdTe QD′s was improved, and 3-mercaptopropionic acid (MPA) modified CdTe QD′s were prepared. As shown in the fluorescence spectra, λex and λem of MPA-CdTe QD′s were found at 320 nm and 558 nm respectively. 17 common metal ions were added to the fluorescence system to test for their effect on the fluorescence intensity of MPA-CdTe QD′s. It was shown that only Cd(Ⅱ) given enhancement effect on the fluorescence intensity while Hg(Ⅱ), Cu(Ⅱ) and Ag(Ⅰ) give quenching effect which can be eliminated by addition of ascorbic acid and KI. Cd(Ⅱ) solutions of various concentrations were added to the reaction system in a buffer medium of pH 6 with 20 μL of MPA-CdTe QD′s as fluorescence probe, after reacting for 6 min, values of fluorescence intensity measured were found to keep linear relationship with concentration of Cd(Ⅱ) in the range of 5.0×10-7-3.9×10-5mol·L-1. Detection limit (3s/k) found was 4.8×10-7mol·L-1.