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In this paper,the altimetry data of ICESat/GLAS was used to approach the precise water level of the Hulun Lake during 2003-2009 to help reveal its variation.The inlier points of 31 tracks were employed by RANSAC process for detailed study to eliminate abnormal values introduced by outlier points.In addition,the NDWI method was proved the most appropriate method to obtain the area of water bodies and was then applied to study the area change of the lake.The research revealed that:(1)In spatially,during the study period,the shoreline of Hulun lake was mainly retreat,especially,in the south area.(2)In temporally,the area of Hulun lake was shrinking fast and the reduced rate is 49.52km2/a in 2003-2009.(3)Water level decreased with volatility from 530.72 m in 2003 to 529.22 m in 2009 and the mean decrement was 0.0759 m/a.(4)The decrement of volume experienced three stages: sharp,slight and then sharp.The general decrement was caused by high temperature,massive evaporation and low precipitation.Reduction of runoff was another reason.Fluctuation or even slight increment of water level was due to the intra-annual temperature drop,decreased evaporation and slightly increased precipitation.Meanwhile,anthropogenic factors including overgrazing and agricultural irrigation accelerated the decrement of water level.The variation of water level at Hulun Lake is a comprehensive result of compound factors of both nature and human beings.