The Qinghai-Tibet Plateau(QTP) is usually regarded as an ideal place to study the response of natural ecosystems to climate change because this mountainous region supports one of the most fragile environments within the global ecosystem. After the QTP experienced a distinct warming in recent decades, scientists have realized that a remarkable variation in vegetation in the QTP could potentially result from climate change. In this paper, the temporal variation of phenology for the alpine Gramineae was analyzed for the dates of the onset of growth in spring, blossoming, and withering from 1988 to 2010 based on the observations from five in-situ sites in the northeastern QTP. Additionally, the relationships between temperature or precipitation and the duration of the growth period for alpine Gramineae were investigated using the stepwise regression and partial correlation analysis. Seasonal trends were found to be advancing significantly in the last20 years in the southern QTP, which includes the Three-Rivers Source Area for the dates of onset, blossoming and withering of grasses. Specifically, the trendsare -4d/10a for onset, -13d/10a for blossoming, and -9 d/10a for withering in the Qumalai fescue grassland, all of which are statistically significant (P< 0.01).Additionally, the Haibei Stipa sareptanavar krylovii grassland, which is in the northern portion of the study area, experienced increasing trends that is totally different with Qumalai for all three phenological events in the last decade. Furthermore, the results revealed significant geographical differences in the observed changes in phonological trends between northern and southern portions of the study area, with a significant advance in the south portion and a weak delay in the northern area for the onset, blossoming and withering of grasses as well as for the overall length of the growing season. The trend in the growing season is similar to that in phenology, with the growing season becoming shorter in the southern area and being extended in the northern area; but the length of the growing season is mainly dominated by the changes of withering dates because the range of phonological change is significantly greater in the withering dates than in the onset dates. Although the onset dates show an advanced trend, which is an advantage in lengthening the growing season, a significant advance of withering dates eliminates the contribution of the earlier onset of the growing season and shortens the overall growing season. The onset dates of alpine grass are strongly related to air temperatures in January and March with negative correlations in the northeastern QTP, while warming air temperatures in January and March lead an advanced onset of growth in grasses. The blossoming dates for the same period in the north have a negative correlation with air temperature, while precipitation with a lead-time of 2 to 3 months is the major factor in southern portion. Moreover, precipitation is an important indicator that influences the withering dates. Precipitation is strongly negatively correlated with withering dates and the previous one to three months of precipitation at Xinhai Station in the northern area, but a weak positive correlation exists between withering dates and precipitation in June with a 2-monthlead time at Gande and Henan stations in the southern area. This indicates that the withering dates will be delayed for a few days when the averaged precipitation occurs in June in the southern area and the significant advance in the withering dates will occur with the above averaged precipitation in May in the northern part of the northeastern QTP.