Abstract: Water is the core of the development and existence of oasis, which is itself the carrier of arid human activities. Therefore, scale and sustainability issues of oasis are closely related with the availability of water in arid regions. This paper examined the Tarim River Basin (TRB) in the arid northwest China as a case study. Based on principles of water and heat balance, a mathematical model for suitable scales of oases was established. The model was used to calculate oasis suitable scale by combining with current hydro-meteorological data. The results indicated that: 1) Because of comprehensive impacts of natural and human factors, oases were still in the process of evolution in time and space. 2) Changes in water resources were the direct driving factors of oasis evolution in both time and space. 3) Water resources were the root restrictive factors of oasis development. With the current water resources supply, available water resources had reached the limit of sustaining the largest oasis scale, and the current cultivated land areas were especially unfavorable to expand for the current oasis scale. Finally, sustainable control measures for stable oasis (e.g., development of water-saving industries, improved irrigation modes, regulated runoff engineering and increased groundwater resources utilization) were put forward. These measures were expected to provide the scientific basis for sustainable management of oasis in arid regions.