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 －0.2～0, 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.