Xinjiang Uygur Autonomous Region (Xinjiang) locates in the arid region of Northwest China. Xinjiang includes 11 grassland types and is one of the five largest pastoral areas in mainland China. Due to climate change and drastic in human activities, we should more focus on grassland ecological security and health. It is necessary to carry out long time series grassland observation based on remote sense. Then, we could further explore spatio-temporal features of grassland, and analyze current environmental pressure on grassland and predict the trend of grassland ecological health. Here, this research was designed to explore spatiotemporal dynamic characteristics of Xinjiang grassland Normalized Difference Vegetation Index (NDVI) on different spatial scales (e.g., Xinjiang, northern and southern Xinjiang, 14 administrative districts and 11 natural grassland types) based on NOAA-AVHRR NDVI dataset from 1981 through 2018, with the method of descriptive statistics, maximum synthesis, and linear regression, respectively. We also analyzed the response of natural grassland NDVI to climate change (e.g., temperature and precipitation) due to correlation and partial correlation. The results illustrate that NDVI of grassland in Xinjiang showed the spatial and temporal variation during the past 40 years, and the responses of Xinjiang grassland NDVI to temperature and precipitation were different. The NDVI of grassland vegetation in Xinjiang showed a slight increase trend with slight interannual fluctuations from 1981 to 2018. After 2000, the interannual variation of grassland NDVI was further decreased. Overall, the Xinjiang grassland NDVI decreased gradually from Ili River Valley, Tianshan Mountains, western Junggar Mountains, Altai Mountains and Kunlun Mountains to Junggar Basin and Tarim Basin. The grassland NDVI, which accounted for 41% of the total grassland area in Xinjiang, showed a significant increase trend. However, 9% of Xinjiang grassland NDVI was a significant decrease trend. Although the grassland NDVI in northern and southern Xinjiang showed a slight increase trend, the water and heat conditions in northern and southern Xinjiang were different. The NDVI of grassland vegetation in northern Xinjiang was 1.4 times that of southern Xinjiang, and the area of grassland vegetation in northern Xinjiang showed a significant increase in NDVI. Correspondingly, the NDVI of grassland in northern Xinjiang was higher than that in southern Xinjiang. The NDVI of grassland types in Xinjiang had a significantly higher response to precipitation than air temperature. Among them, the NDVI of temperate desert grassland, temperate desert-steppe grassland, and temperate steppe grassland had significantly higher responses to precipitation changes than other grassland types, and precipitation had a greater impact on grassland NDVI. Our results indicated that the change of surface moisture caused by precipitation was an important limiting factor for grassland vegetation growth. Since the 1980s, climate in Xinjiang has been warming and humidifying. In this background, this research analyzed the response of grassland vegetation NDVI to temperature and precipitation in the same period. However, the impact of temperature and precipitation changes on Xinjiang grassland NDVI is particularly complicated, especially at different temporal and spatial scales. In the next step, it is necessary to be studied by using multi-source datasets to carry out long-time series scenario simulation.