The interaction mechanism of pentachlorophenol with humic acid (HA) was investigated by the fluorescent quenching effect in this paper. The results showed that the fluorescence of HA was quenched regularly by the pentachlorophenol, and the mechanism of the fluorescence quenching was also studied. Furthermore, the binding constants and thermodynamic parameters of pentachlorophenol with HA were obtained at different temperatures. The hydrogen bonds and van der Waals'forces played...