Abstract: Silurian outcrops include Llandovery Series and Wenlock Series in Zhangjiajie area. In the mudstones of Llandovery Series, the contents of different compositions are as follows: the average content of SiO₂ is 61.59%, the average value of SiO₂/Al₂O₃ is 3.63, K₂O/ Na₂O is 4.80, Al₂O₃/(K₂O+Na₂O) is 3.49, the average content of ∑REE is 238.58×10^-6,the average content of LREE is 213.89×10^-6, the average value of LREE/HREE is 8.68, the average content of B is 98.29×10^-6,the average value of B/Ga is 3.99 and the average value of Th/U is 5.61. According to the tectonic setting discrimination diagrams,the authors declared that the mudstones source of Llandovery Series is active continental margin, interfused with some continent island arc. And the older source could be passive continental margin. The authors concluded that after the combination of Cathaysia and Yangtze Plate, the new plate continued to extrude northwest and formed many uplifts (Qianzhong and Xuefeng uplifts). With further extrusion, Xuefeng uplift was raised above the sea level, which provided argillaceous sediment for Zhangjiajie area. The extrusion caused the formation of island arc and provided part source.