Abstract: An exactly analytical method is needed to detect the thorium in nuclear products. The nuclear sample is complexity, strong radioactivity, and toxicity. It should be separated before be measured. The separate conditions of Th(Ⅳ) with coexisting ions such as UO₂²⁺, Fe³⁺, Zr⁴⁺ etc. by CL-TBP resin were studied. A new fluorescence analysis method for the determination of thorium was developed. The linear ranger is 0-500μg/L and the detection limit is 0.1μg/L. For samples as 1μg/L and 50μg/L, precisions are 2.5% and 0.6%. For simulate sample, the relative standard deviation is 3% and the recovery is between in 92%-100%.