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Vegetation dynamics are an important topic in the field of global environment change, which is of great significance to monitor temporal-spatial variability of desertification at regional or global scales. Following the reported desertification reversion in the late 1990s in the Horqin Sandy Land, an issue was concerned for desertification control by decreased water availability. To detect the desertification process, MODIS Normalized Difference Vegetation Index (NDVI) sequences were investigated to analyze the effect on vegetation over the 2000-2015 growing season. Results showed that: (1) NDVI sequences exhibited a positive trend in most of the significant pixels (19.1%-44.7% of the total), particularly in the southeastern part of Horqin, while showing a negative trend of 2.2%-4.3%; (2) NDVI was weakly related to precipitation since 2000, because intensified anthropogenic activities have obscured the impacts of climate variables, with a rapid decrease in grassland, and increase in cropland and woodland; and (3) the improved NDVI was interpreted by expanding cropland and excessive groundwater irrigation, according to the positive effect of grain yield on NDVI all over the Horqin area. For persistent desertification reversion, a land use strategy should be more adaptive to the carrying capacity in this agro-pastoral transitional zone, particularly with respect to water capacity.