Water-soluble mercaptoethylamine (CA) stabilized CdTe (CA-CdTe) quantum dots (QDs) are synthetized by hydrothermal synthesis method, and the fluorescent responses of as-prepared CA-CdTe QDs to different metal ions are studied. Based on the selective fluorescence quenching of Cu2+ to CA-CdTe QDs, the fluorescent responses of CA-CdTe QDs with particle sizes of 3.27 nm and 3.60 nm to Cu2+ are studied. The study results show that the fluorescence quenching process of Cu2+ to CA-CdTe QDs can be described well by Stern-Volmer fluorescence quenching equation. There is a good linear relationship between the fluorescence intensity F0/F and the concentration of Cu2+ when the concentration of Cu2+ is in the ranges of 4×10-6～44×10-6 mol·L-1 and 1.6×10-6～40×10-6 mol·L-1. The linear correlation coefficients are 0.9876 and 0.9964 respectively, and the detection limits are 8.30×10-7 mol·L-1 and 5.08×10-7 mol·L-1 respectively. The study results also show that the difference of particle sizes of CA-CdTe QDs could not affect the detection and analysis of Cu2+. The fluorescence method of detecting Cu2+ based on CA-CdTe QDs is simple, rapid and sensitive, which can be used well for analysis and detection of Cu2+ in actual water samples.