Silurian of Northern Qilian Mountains- Hexi Corridor consists of the Early Silurian Lujiaogou Conglomerate and Formation, the Middle Silurian Quannaogoushan Formation and the Late Silurian Hanxia Formation. Devonian consists of the Early and Middle Devonian Laojunshan Formation and the Late Devonian Shaliushui Formation. Lujiaogou Conglomerate is intermittently distributed over the western section of the Northern Qilian Mountains and is the deposits of submarine alluvial fan. Angzanggou Formation is widely distributed over the Northern Qilian Mountains- Hexi Corridor and is mainly bathyal flysch deposits. Quannaogoushan Formation and Hanxia Formation are distributed the western regions of the Northern Qilian Mountains- Hexi Corridor. Quannaogoushan Formation is composed of the neritic deposits of sandstone, mudstone and marlite, and Hanxia Formation of the littoral and neritic sandstone and mudstone. Laojunshan Formation is dispersed over the piedmont and intermountainous basin of paleo-Qilian Mountains and is composed of coarse clastic molasse. Shaliushui Formation is distributed over the eastern region of the Hexi Corridor and is composed of sandstone and mudstone of lacustrine facies. Silurian and Devonian regional palaeogeography is controlled by the irregular orogenic process of North Qilian from Caledonian to Early Hercynian. Lujiaogou Conglomerate is the sedimentary response to arc-continental collision during the earliest of Silurian. In the Early Silurian，the Northern Qilian Mountains- Hexi Corridor transforms from back-arc survival basin to foreland basin. In the middle and late Silurian, the orogeny in eastern part of North Qilian is strong. Connection between the eastern part of the orogenic belt and Alashan paleo-continental formed a disintegrating area. Foreland basin is merely located in the western region of North Qilian and Hexi Corridor. The Latest Silurian is main orogenic stage of North Qilian. Devonian Qilian mountains is high and the Early and Middle Devonian molasse formed in the piedmont and intermountainous basin of paleo-Qilian Mountains. In the Late Devonian the orogenic process is strong in the western part of the orogenic belt and formed a disintegrating area. The Late Devonian deposits of lacustrine facies formed in the eastern region of the Hexi Corridor.