Abstract: Setting ecological protection goal of Ulungur Lake is the foundation of the rational and efficient allocation of water reso nrees in this watershed.Baced on the characteristics of breeding of freshwater fish in cold water,the paper puts forward a new approach suitable for the lake in arid area on how to determine the lowest ecological water level subject to the relationship among the lake salinity,fishes and water quantity.According to the new approach,the ecological water demands for reserving the lowest ecological water level in typical years are calculated.The result shows that the lowest ecological water level of Buluntuo Lake is 476.12 m,while,Jili lake is 478.12 m.Deducting the precipitation and 400 million m³ of water diverted from outside river basin,there is still a deficit with an amount of 644 million m³,533 million m³,220 million m³ and 106 million m³ respectively by the year with precipitation frequency of 92%,81%,46% and the normal.Finally,an analysis on the reliability of results is done.