Abstract: Nonwoven geotextile as filter is widely used in the drainage installations of tailings fill dams. But clogging problem of geotextile has been found in some cases. In this paper, regarding the clogging problem happened in Wushan copper mine, a preliminary study on chemical clogging of geotextile through a series of laboratory experiment have been performed. The results show that the adherence of ironic hydroxide jel to the fiber of geotextile is the main mechanism of chemical clogging and the essential condition of serious chemical clogging is that the filter is located in unsaturated or cyclic saturated unsaturated seepage zone as well as enough of fine grained pyrite exist in tailings sand.