Abstract: Youjiang River Valley in Tianyang County of Baise 
City, Guangxi, China, is taken as the research sample area, and the normalized differencewater index (NDWI) of remote 
sensing images of GF-1 and Landsat8 for this Karst area is quantitatively analyzed to provide important 
scientific support for the study of Karst water resources. Specifically, the valley basins and 
Karst rocky mountains in the Karst valley are selected as the study areas. Firstly, the normalized 
water index (NDWI) of the two types of remote sensing images are calculated respectively. Then 
combined with visual interpretation, the accuracy of water body identification and normalized 
water body index of the two types of images are compared. At last,the quantitative relationship 
between normalized water index of images is quantitatively analyzed and compared. The results 
show that the high-resolution images of GF-1 are superior to those of Landsat8 in valley and 
mountain areas, especially for the recognition of mixed directional elements. As for the 
threshold of water identification, the mixed pixels of high-resolution images are mostly 
between 0.6 and 0.8, and the NDWI values of water bodies are mostly around 1.0. The mixed 
pixels of Landsat8 are in the range of $-0.2\sim$0, and the NDWI value of water body is more than 0. 
In addition, the NDWI values of the two images have a certain linear relationship, but the 
quantitative regression results are not so satisfactory. It seems that both GF-1 and Landsat8 
are qualified for identifying mountain topography and valley zones in Karst area, however,
the estimafion accuracy and effect of GF-1 are better than Landsat8.

Key words: Karst area, GF-1, Landsat8, normalized difference water index