CdTe quantum dots(QDs) with high luminescent is synthesized in aqueous phase through one step which is capped with mercaptopropionic acid (MPA) and sodium citrate. As it is found that the fluorescence of CdTe QDs can be quenched by Cu²⁺, the quantitative analysis of Cu²⁺ has been established. The effects of pH value, concentration of the buffer, time of reaction and the concentration of QD are investigated. Under optimal conditions, it is found that the linear range is from 0 to 5×10⁷ mol/L and the limit of detection is 1×10⁸ mol/L.