We extracted vegetation phenology parameters (start, end and duration of the growing season) using GIMMS NDVI remote sensing data from 1982-2005 from the Tibetan Plateau and analyzed the spatial distribution and inter-annual variation of vegetation phenology in order to explore the mechanisms of the response of phenology to climate change. The spatial distribution of vegetation phenology was closely related to hydrothermal conditions on the Tibetan Plateau. Along a transect running from the southeast to the northwest, the start of the growing season was gradually delayed, the end of growth season advanced while the length of growing season reduced. The inter-annual variability of the start and the end of the growing season tended to increase while that of the growing season length decreased. Elevation plays an important role in the regional heterogeneity of phenology, but a boundary was identified at approximately 3400 m altitude. Below 3400 m phenology fluctuated irregularly with altitude whereas above 3400 m phenology was closely associated with altitude. Based on climate data from meteorological stations, the relationship between vegetation phenology and the key meteorological factors under the different grassland types were analyzed; the results show that temperature is more important to the change of vegetation phenology than precipitation on the Tibetan Plateau.