The elements and hydrogen and oxygen isotope geochemistry analysis of oilfield water in the Tertiary in western Qaidam basin shows high salinity and abundant ions of potassium ,boron and lithium of industrial mining grade .The anal-ysis also reveals a hydrogen isotope value distribution of 75.61‰to 13.35‰and an oxygen isotope value distribution be-tween -7.68‰and 10.58‰.Combining these results with chemical analysis of the water ,we concluded that the water was of typical terrestrial origin and was sourced from meteoric water ,which seeped down along deep faults and was in-fluenced by deep-sourced magmatic fluids during its “deep circulation”.The high salinity of the water may be caused by dissolution of saline minerals and their concentration through evaporation .Potassium,boron and lithium are mostly con-trolled by deep-sourced fluids and ions like Ca 2+and HCO3-are mainly sourced from dissolution of carbonate minerals . High concentration of calcium ion and low concentration of bicarbonate radical are thought to be linked to replacement of calcite by dolomite and dissolution of calcite .The formation of CaCl 2 type water is therefore inferred as the result of an ad-equate water-rock reaction and the participation of deep-sourced fluids .It is preliminarily inferred that the Tertiary in Nanyishan area of the basin may be a potential target for exploration of potassium .%柴达木盆地西部第三系油田水具有高矿化度特征，钾、硼、锂等离子达到工业开采品位，氢同位素值分布在-75.61‰～13.35‰，氧同位素值分布在-7.68‰～10.58‰。综合分析油田水化学成分、水化学参数组合以及氢氧同位素特征推断：柴达木盆地西部第三系油田水起源于大气降水，为典型陆相成因，为大气降水沿深大断裂下渗并经历了“深循环”作用形成，同时有深源岩浆流体的参与。油田水高矿化度特征与盐类矿物溶解和蒸发浓缩有关，钾、硼、锂等元素受深源流体控制，Ca2＋和HCO3-主要来源于碳酸盐矿物溶解，油田水高Ca2＋、低Mg2＋的特征与演化过程中白云石交代方解石以及方解石溶解有关，充分的水-岩反应与深源流体的加入导致柴达木盆地西部第三系深成CaCl 2型油田水的形成。同时，初步推断南翼山地区第三系可能具有找钾意义。
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