The aim of this study is to analyze the trend of vegetation changes in Iran over a 20-year period from 2000 to 2020 using the Normalized Difference Vegetation Index (NDVI) obtained from MODIS satellite data. So, the monthly Normalized Difference Vegetation Index (NDVI) of 2000, 2010, and 2020 for the period 2000-2021 is used to study vegetation cover. These images are obtained from the MODIS Terra Sensing Satellite (MOD13A2). Therefore, to analyze the trend of changes in the monthly NDVI time series data and process them in the GIS software environment, the NDVI index was divided into 5 classes. An examination of the average annual changes in the NDVI index from 2000 to 2020 showed that the highest value of this index was observed in different years in the northern, northwestern parts, and sporadically in the western and southwestern parts of Iran. An examination of the changes in the NDVI index over a 20-year period showed that in the entire area of Iran, this index increased in about 25% of the study area and decreased in about 75% of it during the period 2000 to 2010, 2010 to 2020, and 2000 to 2020, respectively. An examination of the NDVI vegetation index in five classes: 0.1 -0.2, 0.2 -0.4, 0.6 -0.4, and more than 0.6 in the years 2000, 2010, and 2020 shows that these classes accounted for 52.61, 39.02, 6.28, 1.21, and 0.88 percent of the study area in 2000, respectively. Also, these classes accounted for 44.28, 35.36, 17.8, 1.62, and 0.94 percent of the study area in 2010, respectively, and 40.05, 39.21,18.08, 1.75, and 0.92 percent of the study area in 2020, respectively. An examination of the percentage changes in the area of different NDVI classes in Iran from 2000 to 2020 showed that during this period, the percentage of the area of classes 0.2-0.4 and 0.6-0.4 increased, and this increase between 2000 and 2020 was about 18.36% and 0.85%, respectively. The study of changes in vegetation classes showed that the NDVI vegetation index was in the classes 0.1-0.2, 0.2-0.4, 0.6-0.4 and more than 0.6, with the highest percentage of vegetation cover in the classes 0.1-0.2, 0.1-0.2, which accounted for 91.63% in 2000, 79.63% in 2010 and 79.25% in 2020, which had a decreasing trend. While the class 0.6-0.4, which included less than 2% of vegetation cover, showed an increasing trend. The highest percentage of vegetation cover was in the classes 0.1-0.2 and 0.1-0.2, which accounted for more than 90% of vegetation cover, and less than 1% of the area of the region was in the class greater than 0.6. In Iran, classes 0.4-0.2 and 0.4-0.6 have had an increasing trend, and class 0.1-0 has had a decreasing trend. The results showed that during this period, a large part of the study area experienced a decrease in vegetation cover, such that only 20.78% increase and 22.79% decrease in NDVI were observed. Also, a decrease in coverage was observed in the lower classes (0.0-1) of NDVI and an increase in the middle classes (0.2-0.4 and 0.4-0.6), indicating an increase in shrub and rangeland cover. This study confirms the effective role of remote sensing in analyzing ecosystem and vegetation changes at large scales.