An effective energy transfer could occur between CdS@ZnS QDs and rhodamine B（RhB)in the presence of Tween 40 in pH 7.6 PBS buffer solution,leading to significant fiurensence qunching of CdS@ZnS QDs（donor) and increase of RhB（acceptor).As adding oxytetracycline,the fluorescence intensity of FRET system decreased because the electrostatic interaction between RhB and oxytetracycline occurred.A good linear relationship was observed between fluorescence quenched intensities and concentrations of oxytetracycline in the range of 4×10-8-60×10-8 mol/L,with a correlation coefficient（r) of 0.999 0 and a detection limit of 1.13×10-9 mol/L.Based on this,a new determination method for oxytetracycline was developed.With a good stability and high selectivity,the method was applied in the determination of proteins in milk samples with recoveries of 97.5%-103.7%and relative standard deviations（n=6) not more than 2.0%.