Abstract: Northern Qinling Mountains and southern Qilian Mountains are located in the middle part of the famous latitudinal Qinling mega-orogenic belt. It belongs to rifted orogenic belt of the Cambrian-Ordovician period. It underwent a series of tectonic opening-closing including intraplate continental rift--intercontinetal rift--volcanic arc--orogenic belt. During the Cambrian, the alkaline and tholeiitie basalt, and also small Ocean basin ophiolite suit were formed under an extension environment. In the Ordovician, the tectonic setting was closing. The intermediate-acidic volcanic rocks of calc-alkaline and shoshonite series, as well as the volcanic are suit rocks were formed. The boninites were also formed at this time. Southem Qilian belongs to the single rift system; however, northern Qinling belongs to the double rift system. In northern Qinling rift system, from east to west and from south to north, the distance of extension decreased, the velocity of closing increased, and the intensity of volcanic eruptions, acidity, K content, crustal materials of volcanic rocks we gradually getting larger. The distance of extension was similar to the Red sea’s; however, the velocity of closing was similar to the Andes type. The characteristics of old mantle ware superimposed. In the Cambrian period the mantle was depleted in crustal materials; however, in the Ordovician period the mantle was enriched in crustal materials. Through the latitudinal comparative research between Dabei Mountains--northem Qinlng--southern Qilian--northern margin of the Chaidamu Basin, we found that the basic and acidic magmas of northern Qinling and southern Qilian were mainly formed through partial melting of mantle and crustal respectively; whereas the intermediate reeks were formed through assimilation- fractional crystallization(AFC)of the basic magama. From east to west, the rift opened gradually; The ages of volcanic eruptions were getting younger; the duration of volcanic eruptions was getting shorter; the rift system changed from single to double character; the distance of extension was getting larger; the velocity of extension and closing Was becoming larger; the alkalinity of volcanic rocks was getting smaller. There was no ophiolite suit in the east, whereas it appeared in the west; The sources of old mantle were changed from mixed DMM and EM-I to mixed EMM and EM-Ⅱ.