The criteria for an acceptable formation watercut level in the western Sulige gasfield in Ordos Basin can be summarized as salinity≥50g/L,sodium-chlorine ratio ＜0. 5 ,sodium-calcium ratio ＜ 1 and fracturing fluid flowback rate ≥3100%. Based on a comprehensive analysis of water formation chemical characteristics, hydrogen and oxygen isotopes as well as trace element" Br" ,the paper concludes that the formation water in the western Sulige gasfield was of continental sedimentary origin and experienced extensive water-rock interaction and evaporation processes. The analysis also indicates that sealing condition for the formation water in the Upper Paleozoic is good, thus which is favorable for gas accumulation and preservation. Further analysis in combination with consideration of hydrocarbon accumulation elements such as source rocks, reservoir and cap rocks reveals that the formation water is residual water from the process of weak dynamic hydrocarbon accumulation. The complicated gas-water distribution pattern is caused by reservoir heterogeneity and microstructures on the background of low hydrocarbon-generating intensity and low tectonic position. The formation water of high salinity in the eastern Ordos Basin is suggested to be related to the water-rock process of the Ordovician salinastone.%鄂尔多斯盆地苏里格气田西区正常地层水的判别标准为:矿化度≥50 g/L,钠氯系数(rNa+/rCl-)＜0.5,钠钙系数(rNa+ /rCa2+)＜1,压裂液返排率≥100％.通过地层水化学特征、氢氧同位素和微量元素溴的综合分析认为,苏里格气田西区地层水来源于经过了强烈水-岩作用和蒸发浓缩作用的陆相沉积成因水.确认苏里格气田上古生界地层水封闭条件好,有利于天然气聚集和保存.进一步结合该区烃源岩、储层和盖层等成藏要素分析认为,该区地层水主要是弱动力成藏过程中的残余地层水,复杂的气-水分布源于低生烃强度和低构造位置背景下储层强非均质性和微构造的共同作用；而盆地东部的高矿化度地层水与奥陶纪盐岩的水-岩作用密切相关.
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