In order to reveal the trend of phenological period and the law of response to climatic factors in the grassland of Xilin Gol League, this paper extracted the phenological period of Xilin Gol League grassland by using the method of double logistic function fitting and dynamic threshold based on the MODIS-NDVI dataset from 2002 to 2014.This study investigated patterns of the spatiotemporal variations in phenology and its possible influence factors. The results show that:(1) During the research period, the grassland greenup of Xilin Gol League showed an early trend, the withering period showed a delayed trend, and the growth period showed an extended trend.(2)In the study area, 25.93% area of the Grassland greenup was negatively correlated with precipitation, 57.24% was negatively correlated with air temperature. Sunshine hours had no significant effect on the grassland greenup. 21.65% area of the Grassland withering period was negatively correlated with air temperature, 22.24% was negatively correlated with sunshine hours. Precipitation had no significant effect on the grassland withering period.