[Objective] The spatio-temporal dynamic changes of vegetation in Tongren City, Qinghai Province (located at the westernmost end of the Loess Plateau and the bordering Qinghai-Tibet Plateau) were studied in order to provide references for ecological protection and management of the transition zone between the two plateaus.[Methods] The characteristics of dynamic vegetation changes in space and time from 2000 to 2019 were investigated using linear trend regression and the Hurst index based on MODIS-NDVI data. Also, a preliminary analysis of relationships between NDVI changes and land uses and altitudes was conducted, and future trends in NDVI variation were predicted.[Results] ① NDVI values in Tongren City showed a growth rate of 0.027/10 yr over the past 20 years. Areas with high NDVI values increased significantly, and were mainly located in the eastern and western mountainous areas. The areas with NDVI values varying between 0.8 and 1.0 increased from 388.63 km² in 2000 to 1 066.92 km² in 2019. ② NDVI increased over an area of 2 925.21 km², accounting for 84.42% of the city's area. This area was widely distributed in the Longwu River valley and the surrounding mountainous area, including 626.13 km² of forest land and 2 094.11 km² of grassland. ③ The area where NDVI decreased was 539.79 km², accounting for 15.58% of the city's area. Most of this area was located in the high-altitude area in the western and southern mountainous area, while a small part of the area was in the Longwu River valley. Taking the lowest altitude of freezing and thawing erosion (3 583 m) as a limit, the area of decreasing NDVI was located above 3 583 m, and accounted for 70.93% of the total area that showed decreasing NDVI. ④ In the future, NDVI will generally continue to increase, with the area of increasing NDVI accounting for 79.17% of the city area, while the area where NDVI will decrease will account for 13.13% of the area of the city.[Conclusion] During the past 20 years, NDVI has generally increased in Tongren City, with high-coverage vegetation increasing significantly. The areas where NDVI decreased were mainly located in high-altitude areas. In the future, NDVI values for Tongren City will continue to increase as a whole, but some areas will still show decreases in NDVI.