The surface modified quantum dots (QDs) as fluorescence probe to quantitatively detect the Pb2+ in water phase was studied in the paper. Using the mercaptopropionic acid (MPA) as the stabilizer, the CdTe quantum dots were synthesized in water phase. Based on the quenching effect of the Pb2+ on the QDs fluorescence, the method for detecting trace Pb2+ using QDs as probe was established. The results showed that the relationship between the Pb2+ concentration and the quenching intensity of the QDs (ΔF) while the Pb2+ concentration ranged from 1.0×10-8 to 1.0×10-6 mol·L-1 was fairly linear, and the correlation coefficient was 0.997 2. The detection limit was 9.3×10-10 mol·L-1. The RSD was 5.9%, and the recovery rate was between 86% and 110%. The study of the interference of the metal ions showed that the method was highly selective.