Abstract: The Tertiary of the West Qaidam Basin was deposited in the environment of a brackish-salt lake basin.The Shizigou saline lake in the west existed from the Paleocene-Eoceneto the Miocene and was dominated by brackish-salt water lake factes,while the saline lake in Nanyishan area existing from the Oligocene to the Pliocene.The developing period of main oil-generating depressions is the Miocene and the Pliocene dominated by the deposit of brackish lake factes.Studies on organic geochemistry show that the organic matter of the Tertiary oil-generating rocks in the west is mainly mix-typed,and part of it belongs to sapropel and humic types.Judged by the'changing relationship of dicyclic aromatic hydrocarbons to polycyclic ones and the relationship of aromatic hydrocarbon compounds to sedimentary environment and mother rock inputs,there is genetic relationship between the naphthalene series,biphenyl series,retene and other compounds in aromatic hydrocarbon fractions and higher terrigenous plants.But phenanthrene series,chrysene series,benzopyren and benzonaphthalene thiophene probably have closer relationship to lower hydrobios.In addition,salt water reduction environment advantageous to the formation of fluorene series and sulfur fluories compounds is also advantageous to the preservation of naphthalene series compounds.