Huangyuan county is located in the eastern part of Qinghai province and is the transition zone of Loess
Plateau and Qinghai-Tibet Plateau. While the ecological environment in Huangyuan county is fragile
and is mainly characterized as serous soil erosion, frequent natural disasters. It is very important to
study the soil erosion. Hudan river basin was selected to study the soil erosion in Huangyuan county.
The soil erosion information was extracted from Landsat 5 TM data in 1987, 2000 and 2010. To
classify and grade soil erosion was according to the classification standard, Classification Standard for
Soil Erosion, issued by the Ministry of Water Resources of the People’s Republic of China.
The types of soil erosion in the basin were classified as water erosion, freeze-thaw erosion and
engineering erosion based on TM imagery, field survey and historical data. Water erosion was the most
important part and accounted for more than 90% of the whole area. Weak water erosion increased
significantly during the period, mainly distributing in the north of the basin. Slight-degree water
erosion increased from 1987 to 2000, while there was a steep reduce during the period from 2000 to
2010. Freeze-thaw erosion distributed mainly in northern areas with high altitude. What Engineering
erosion affected were narrow valley areas suitable for human settlements and agricultural production.
The Digital Elevation Model (DEM) are terrain elevations at regularly spaced horizontal intervals, i.e., an a
grid of regularly spaced elevations. With the development of computing technology, the methods of data
acquisition, data storage and data processing speed for DEMs get along well. Heihe river lies in the northwest
of China and is a continental river. It roots from snow-ice and disappears in deserts. The drainage area is about
140,000 square kilometers and the river is the main water source for the living. The upper reaches are
mountainous and the runoff is very important. The middle reaches are oasis. At present, many hydrological
and ecological models are introduced. The catchment basin and stream network data acquired from DEMs are
main input data for many surface hydrological models. So the quality and resolution of DEMs are significant.
Software ENVI Version 4.2 furnishes with the DEMs Extraction Module. The paper compared several
methods for extracting DEMs of the upper reaches. We extracted the elevation data from the ASTER---stereo
images with the module and created the DEM. Secondly; we collected the DEM based on the contour map of
Heihe river. The comparison of the DEMs quality was carried out between the DEM from the contour map,
the DEM extracted by ENVI Version 4.2. To a certain extent, the DEM from Aster imagery can reflect the
terrain and be used in hydrological models.