The Lower Reaches of the Tarim River is featured with an extraordinary dry and hot climate.Vegetation here has a harsh environment to survival,and water is the most crucial ecological factor.The research of water sources used by desert plants in the growing season helps to understand the water use strategy of the desert plants,which will be useful to vegetation reconstruction in the Lower Reaches of Tarim River.In this study,the stable oxygen isotope(delta18 O)of stem water of four dominant plant species,groundwater and soil water in the lower reaches of Tarim River were measured in May,July,August and September,2015.And then we used the Multi-source mixed liner model(IsoSource)to analyze the probable contribution of potential water sources used by these dominant desert plants.In addition,we use the proportional similarity index(PSI)to analyze the water use relationship between different desert plants.The result indicated that:(1)in the Lower Reaches of Tarim River,Populuseuphraticaoliv(young and mature)and Tamarix ramosissima can hardly use soil water stored at 0-50 cm depth,but mainly uptook deep soil water stored below 200 cm depth and groundwater,Gly-cyrrhizainflataand Alhagi spar folia mainly acquired soil water stored at 50-200 cm depth.(2)During growing season,P.euphratica oliv(young and mature)and T.ramosissima had a fierce water competition,except for individual months.lycyrrhiza inflata and Alhagi spar folia also had a strong water competition,however,P.euphratica oliv(young and mature)and T.ramosissima had a weak water competition with G.inflataand A.spar folia.(3)In order to adapt extremely drought environment,P.euphratica oliv(young and mature)and T.ramosissima had a stable water sources,and the feasible proportion of water sources used by different plants had a slight fluctuation in the Lower Reaches of Tarim River.