Se is a necessary trace element for human and animals,but the excess intake of Se caused poison.Thus,it is very important to determination of Se in foods and water.The target of this study is development of a new,sensitive and selective hydride generation-molecular fluorescence method for the determination of Se.In 0.36 mol·L-1 sulfuric acid,NaBH4 as reducing agent,Se(Ⅳ) is reduced to H2Se.Using I-3 solution as absorption liquid,I-3 is reduced to I- by H2Se.When adding rhodamine 6G,Rhodamine 6G and I-3 form association particles,which lead to the fluorescence intensity decreased .When Se(Ⅳ) existing,Rhodamine 6G and I-3 bind less,And the remaining amount of Rhodamine 6G increase.So the fluorescence intensity is enhanced.The analytical conditions were optimized,a 0.36 mol·L-1 H2SO4,21.6 g·L-1 NaBH4,23.3 μmol·L-1 rhodamine 6G,and 50 μmol·L-1 KI3 were chosen for use.When the excitation wavelength is at 480nm,the Rayleigh scattering peak does not affact the fluorescence recording,and was selected for determination of Se.Under the selected conditions,Se(Ⅳ) concentration in the 0.02～0.60 μg·mL-1 range and the increase value of the fluorescence intensity(ΔF) at 562 nm linear relationship.The linear regression equation is ΔF562 nm=12.6ｃ+20.9.The detection limit was 0.01 μg·mL-1.The influence of coexistence substances on the hydride generation-molecular fluorescence determination of 5.07×10-6 mol·L-1 Se(Ⅳ) was considered in details.Results showed that this new fluorescence method is of high selectivity,that is,0.5 mmol·L-1 Ba2+,Ca2+,Zn2+ and Fe3+,0.25 mmol·L-1 Mg2+,0.05 mmol·L-1 K+,0.2 mmol·L-1 Al3+,0.025 mmol·L-1 Te(Ⅵ) do not interfere with the determination.The influence of Hg2+,Cd2+ and Cu2+ that precipitate with Se(Ⅳ),can be eliminated by addition of complex reagent.This hydride generation-molecular fluorescence method has been applied to determination of trace Se in water samples,with a recovery of 91.8%～107.1%.