Abstract: The Mangya Depression in the western part of the Qaidam Basin is the major Tertiary hydrocarbon-producing area of the basin. There distributes the highest gas and oil fields above sea level in the world It is a megadepression evolving from a Mesozoic back-arc paraforeland basin to a Cenozoic intermountain basin, and filledwith large sets of argillaceous rock,calcareousmudstone,carbonate rock and clastic rock of saliniferous-semisaliniferousenvironmentunder the semidry clinateof inland lakeswhich foam a set of giant-thick hydrocarbon source rock w ith two periods of hydrocarbon expulsion peaks, two types of reservoir series aswell as special capping and migration conditions The different allocation of variousoil-generating elements in tine and space constructs the Mangya Depression a large scale of first-order petroleum system constituted by at least five secondrorder petroleum system s Each second-rder petroleum system show smultip1e superposition and intersection in space, and connects continuously and develops layer by layer in tine,By analyzing on thepetroleum system sof the area, it is suggested that the exploration direction of the next step should be mainly deep targets, especially the three zones, the one slope and lithos-tratigraphic gas and oilpools