The fluorescence spectrum was studied for the chlorothalonil(0.292 8 mg·mL-1) using spectrofluorophotometer. The experiment results showed that the characteristic peaks (352 and 366 nm) are found in the spectrum of chlorothalonil standard solution when the excitation wavelength is 320 nm. And it was found that the shoulder peak gradually disappeared at 366 nm, while the fluorescence peak is stable at 352 nm with the decline of the solution concentration. The exponential functional relationship between the concentration of chlorothalonil and fluorescence intensity at 352 nm was obtained, and its correlation coefficient is 0.999. The experimental results are consistent with the theoretical formula about fluorescence intensity and concentration. The prediction model functions were also obtained through the liner fitting to the chlorothalonil solution of low concentration, and the correlation coefficient is 0.995. The limit of detection (LOD) is 0.018 8 μg·mL-1, the limit of quantification (LOQ) is 0.062 7 μg·mL-1, and the linear range is 0.062 7～28.45 μg·mL-1. And fluorescence spectra were studied for the mixed system of astragalus, medlar and chlorothalonil. It was found that the fluorescence intensity of chlorothalonil solution is all declined with the addition of two kinds of Chinese Herbal Medicines, which indicates that there is an interaction between them. The decay rate of fluorescence intensity was obtained which is 88.5% and 99.7%, respectively. Then the model functions were established between fluorescence intensity and the volume of addition, and the correlation coefficient is 0.994 and 0.997, respectively. This study provides the experimental foundation for the detection of chlorothalonil residues using fluorescence spectrum. It is shown that it is possible to detect pesticide residues of chlorothalonil using fluorescence spectra directly, and the relevant parameter value satisfied the requirement of testing standard. Therefore there is an important value for further detecting the pesticide residues in fruit juice using fluorescence spectrum. It was also found that the fluorescence intensity of chlorothalonil is decreased with the addition of astragalus or medlar, which provides the new research approach to studying the pesticide degradation using medicinal and edible Chinese Herbal Medicines.