Abstract: Abstract: Using time series MODIS-NDVI dataset in growing season from 2000 to 2013 and precipitation, temperature, evaporation and wind speed data, dynamic change of aeolian desertification and its response to regional climate change in Horqin sandy land at the beginning of 21st century were studied in this paper. A dimidiate pixel model was chosen to calculate the vegetation coverage index (VCI), and aeolian desertification index (ADI) was established on the basis of negative correlation between VCI and aeolian desertification degree. Then, a classification system of ADI was developed by the decision tree method. In addition, linear regression was used for the temporal trend analysis of ADI and the selected climate factors. Mann-Kendall statistical test was used to estimate the significance of the trends. To reveal the effects of climate change on aeolian desertification further, this study analyzed the correlation between climate factors and aeolian desertified lands at an administrative scale using Pearson's correlation analysis method. The result showed that the aeolian desertification underwent a process of reversion-development-reversion in Horqin sandy land at the beginning of 21st century, among which the area of aeolian desertified lands decreased in periods from 2000 to 2005 and from 2009 to 2013 and increased from 2005 to 2009. The areas of slight and medium aeolian desertified lands changed in a significant downward trend. The areas of serious and extreme serious aeolian desertified lands changed in a non-significant downward trend. The non-aeolian desertified lands were mainly distributed in the northwest parts while the serious and extreme serious aeolian desertified lands were in the southwest parts of the study area. The slight and the medium aeolian desertified lands were wildly distributed in the northern, eastern and the southern parts of the study area. The precipitation was on the rise while the temperature, evaporation, and the windy days driving sand were on the decline with the trends slope of 8.34 mm/a、?0.04℃/a、?23.56 mm/a and ?1.7 d/a, respectively, among which the downward trends of evaporation and the windy days driving sand were significant. In spatial distribution, areas where the precipitation increased strongly were manly distributed in northeast and northern part while the areas where temperature decreased obviously were in the west and southeast of the study area. Areas where evaporation decreased significantly were distributed in the center and southeast part (around Horqin district and Jarud Banner) and that of windy days driving sand was in south, southeast and eastern part of the study area. Aeolian desertification in Horqin sandy land was mainly affected by hydrothermal condition, especially in the 2 periods of 2000-2005 and 2009-2013. The increase in precipitation and the reduction in evaporation made regional climate more humid, and the twice reverse of aeolian desertification. Reduction in evaporation was closely connected with the temperature decrease. Although the windy days driving sand declined significantly, it had little effect on aeolian desertification. In addition, climate impact on desertification had regional differences, and the areas where were affected by climate were mainly concentrated in the eastern and southeastern parts of the study area.