Abstract: Salicylic aldehyde thiosemicarbazone was quenched by Cr(Ⅲ) in the medium of ammonium chloride and ammonia,the degree of quenching increases with the content of nitrite ion increases.A method based on fluorescence quenching for determination of trace Cr(Ⅲ) was proposed.The detection limit was 13.6 μg/L and the linear range of determination is 20.0～220.0 μg /L.The proposed method is simple and highly sensitive for determination of trace Cr(Ⅲ) in water samples of industrial,water supply and well.