Samples of Alhagi sparsifolia and Nitraria roborowskii leaves were colleted on the south fringe of the Taklimakan desert.At different relative water contents (RWC),we investigated the characteristics of the water potential (ψ_w),stomatal conductance (G_s) and chlorophyll fluorescence parameters changes.The results indicated that:(1)Under the dehydration stress,the initial G_s value of N.roborowskii was high as 495.7 mmol·m^-2·s^-1 and decreased slowly when RWC above 96%;While A.sparsifolia’s stoma responded quickly to the dehydration stress,it could control the G_s value in 180 mmol·m^-2·s^-1 and had a generally slow decrease.(2)N.roborowskii’s initial water potential was higher than A.sparsifolia’s and could maintain some stability in extent,but when RWC below 84%,its ψ_w began to decrease strongly under the level of A.sparsifolia’s,which always maintained more slowly.(3)The two’s leaves G_s to absolute ψ_w showed negative exponential regression relationship and there was a critical point of ψ_w to G_s of N.roborowskii as -2.2 Mpa,but A.sparsifolia had no clear point.(4)On the natural dehydration,both two showed F₀ rose significantly,F_v/F_m,F_v/F₀ values decreased.N.roborowskii had more severe damage to reaction centers,but A.sparsifolia’s F_v/F_m value more than 0.1 until RWC was 55%,indicating it’s PSⅡ reaction centers itself was stable,meanwhile,its TR_o/RC,RC/CS_o values posed fluctuate and its RC/CS_o changed insignificantly.N.roborowskii’s fluorescence specific activity values increased suddenly and the fluorescence curves distorted when RWC less than 78%.In summary,A.sparsifolia posed low water potential to tolerate dehydration and it may exist reaction centers lose activity reversible and energy trap to carry on heat dissipation and respond water stress,while N.roborowskii showed maintain high water potential to delay dehydration and its RWC point which stands for water stress utmost threshold was 78%.In all,A.sparsifolia as local dominant species have a better adaptability and tolerance and N.roborowskii is not suitable for the area to introduce and spread where or long term consistent drought or groundwater level fluctuates strongly exist.