The Bosten Lake is the largest inland freshwater lake in China, which is also the important freshwater resources in the southXinjiang. Since the 1950s, the water level of the Bosten Lake has undergone several drastic changes, especially in the past 30 years, it hasbeen particularly volatile, and it has caused a great negative impact on the local economic construction. Based on the principle of waterbalance, after an analysis of meteorological and hydrological data of the Bosten Lake Basin during 1986-2012, it figures out that the sharprise in water level of the Bosten Lake during 1986-2002 was caused by the increase in runoff of the Kaidu River and the reduction of thewater diversion of irrigation area at the Kaidu River. From 2002 to 2012, the runoff of the Kaidu River continued to decline, and the overexploitation of groundwater caused the increase of the channel loss of the Kaidu River, and the pumping water of the Bosten Lake increasedyear by year. The interaction of these factors led to the sharp decline of the water level of the Bosten Lake.