[Objective] The temporal surface ecological spatial changes and climate-driven characteristics of China’s inland arid grassland at the county scale was determined in order to provide a scientific basis for the formulation of reasonable ecological measures. [Methods] This study was conducted in Sunan County (Yugu Autonomous County of Sunan), Gansu Province. Normalized difference vegetation index (NDVI) and meteorological data were collected and analyzed to determine the characteristics and driving factors of the temporal and spatial changes of vegetation NDVI in Sunan County from 2001 to 2020 using trend analysis, variation analysis, partial correlation analysis, and residual analysis. [Results] ① During the study period, NDVI for the county showed a fluctuating upward trend, with a rising rate of 0.042/10 yr. In addition, the NDVI of the 10 vegetation types showed a similar growth trend that was reflected more accurately than in previous small-scale regional studies. ② NDVI gradually increased from northwest to southeast. The NDVI variation trend was basically stable in 36.14% of the area of Sunan County, while the degraded area was much larger than the improved area. ③ The contribution degree of the different vegetation types to NDVI stability in Sunan County followed the order of coniferous forest>scrublands>broadleaf forest>steppe>meadow>alpine vegetation>cultivated vegetation>others>swamp>desert. ④ NDVI was most affected by summer precipitation and plant growing season temperature. Human activities had a facilitating effect on 96.52% of the vegetation NDVI in Sunan County. [Conclusion] Overall, the vegetation NDVI of Sunan County has increased over the past 20 years, and its change trend was influenced by both climatic conditions and human activities. In the future, vegetation NDVI in the overgrazed areas of Sunan County may continue to decline, but the overall trend will be increasing.