| The lake water are important component of global water resources, are closely related with human survival and development, nowadays lake water sharply reduced, water pollution and eutrophication were getting worse. Hulun Lake is located in the Inner Mongolia grassland, is an important ecological barrier of northern China. In recent years, the water level droped , area dwindling in Hulun Lake year by year, have affected the fishing and the surrounding ecosystem seriously, and causing the Hulunbeier grasslands change desertification constantly. This paper was studied of the water dynamic change in Hulun Lake, the conclusions as following:(1) By extracting and analysis the digital river network and basin boundary based on DEM. The Hulun Lake Basin were distributed widely range, including of seven sub-basins, the basin total area are 202,000 km2, accounted of 19.3% in China, 80.7% in Mongolia.The terrain analysis showed, 60% of the area are flat grassland, the steep slope and acute slope are small proportion, mainly in Mongolia, these regions the runoff conditions are good. The above indicates, the amount of water into our country from Mongolia were determine the expansion or contraction of Hulun Lake.(2) In order to explain the change of Hulun Lake suface, selected image data nearly 24 years to research. After pretreatment, to analysis the band reflected spectrum and correlation, showed the band 4 had considerable independence, the correlation coefficient with other band were minimum. Analysis three methods of False color composite image to determine choice the color RGB = 742 image was water extraction image. Extract result showed more changes were concentrated in the lower left corner and the east coast of lake beach in Hulun surface area.(3) Application the solar radiation band and thermal infrared radiation band to establishment water depth retrieval model. After the model calculation showed, model average absolute error were 0.2m to 0.6m, average relative error were 6% to 13%, the logarithmic models on the optimal model. The sensitivity analysis showed that the band 6 has maximum sensitivity, the contribution of band 6 was largest, also confirmed the theory correctness of thermal infrared band retrieval water depth. Through band math operation to acquired the water depth distribute results of all lake, and 2007-09-24 was the best year.(4) Application the results of water depth to maked vector operation, final generated the three-dimensional TIN model of Hulun Lake. Then using 3D analysis tools to calculate TIN model, got the relationship of water level and area, volume. Take visualization operations for TIN model, showed the 3D state of Hulun Lake change process under different water level.(5) The long time series water balance analysis of Hulun Lake showed, The water supply addition to precipitation and river flow should be have groundwater recharge, The main reason for the Hulun Lake dwindling was river runoff reduction, Hulun Lake region's climate was drying trend.(6) According to the findings of full text and the current lake protection and management experience, finally give some countermeasures and suggestions for protect the Hulun Lake, look forward to provide some basis for decision makers.
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