Temporal sequential analyses of the hydrological observational data in the Tarim Basin over the last forty years revealed an annual increase of 2×10 7 m 3 in the water quantities at the three headstreams of the upper courses and an annual decrease of 3×10 7 m 3 in the water flow from Alaer, which is on the upper main stream. A prediction of the trends indicates that there can be severe situations under which intermittent water interceptions occur. By means of approximate estimations on vegetative water consumption through phreatic evaporation combined with a quota assessment, the ecological water demands required to maintain the ecological environment in the mainstream area over the three different targeted years of 2005, 2010 and 2030 are defined as standing at 31.86×10 8 m 3 , 36.27×10 8 m 3 and 41.04×10 8 m 3 respectively. Ecological fragility indexes are established on the basis of the selection of environmental sensitivity factors. Rational evaluations give proof that the lower reaches of the mainstream have already turned into zones where their ecological environments are gravely damaged. Multi-objective optimization should be conducted and protective schemes be framed within the threshold limits of the bearing capacities of water resources and the environment.