The present work is to find the optimum condition for fluorescence resonance energy transfer between CdTe QDs (donor) and rhodamine B (acceptor) and form a new method to detect copper in Flos Lonicerae Japonicae. In tris-HCl buffer solution at pH 6.00, by employing cetyltrimethylammonium bromide, Cu2+ can quench the fluorescence intensity of BRB and detect the concentration of Cu2+. Results show that a linear relationship could be established between the quenched fluorescence intensity of RhB and the concentration of Cu2+ in the range of 1.3×10-4～3.1×10-2 μg·mL-1, the limit of detection was 4.6×10-5 μg·mL-1 (r=0.996), RSD and the average recovery was 3.5% and 103.4% (n=5), respectively. It is concluded that the developed method was proved to be feasible to detect copper in Flos Lonicerae Japonicae.