Abstract: Based on MODIS-NDVI data,the temporal and spatial variation characteristics of the normalized vegetation index（NDVI） during the main growing season（May-September） in Yili River Valley during 2001-2020 were studied by Theil-Sen median trend analysis,Mann-Kendall test and coefficient of variation method.The influencing factors of vegetation growth season were explored.The results showed that:（1）There was a significant spatial difference in NDVI during the main growing season in Yili River Valley from 2001 to 2020,and the average value of NDVI was higher in multiple years.（2）At the regional scale,the interannual variation trend of NDVI was relatively flat. At the pixel scale,the areas of micro decreases and micro increases were relatively large,while the areas of significant increases and decreases were relatively concentrated and small.（3）Vegetation stability was good in Yili River Valley from May to September（main growing season）.Regions with CV≤ 0.10 were distributed in the whole vally,and regions with 0.3＜CV≤1 were concentrated.（4）From 2001 to 2020,the temperature in Yili River Valley showed an increasing trend,while the precipitation showed a slow decreasing trend.The NDVI annual mean had a significant correlation with annual precipitation（r =0.764 4）,and no significant correlation with temperature;the NDVI monthly mean was strongly correlated with the monthly mean temperature,and weakly correlated with the monthly precipitation.