Alpine meadow and alpine steppe are two important vegetation types on the Qinghai-Tibet Plateau. Studying the correlation between vegetation change and climate change in alpine meadow and alpine steppe is helpful to provide reference for the management of the two alpine grassland ecosystems on the Qinghai-Tibet Plateau in response to global climate change. In this study, the alpine meadow of the Three-River Headwaters Region and the alpine steppe of Ali located in the same latitude were taken as the research objects. Vegetation changes were characterized based on the changes of Net Primary Productivity (NPP) of vegetation. Based on NPP data and meteorological data, the spatial and temporal variations of NPP, precipitation and air temperature between 2000 and 2017 were analyzed. Sen+ Mann-Kendall trend test was used to study the change trend of climate and vegetation net primary productivity in two alpine grasslands. The effects of grazing activities on the vegetation change of alpine grassland were studied by using the yield of beef and mutton in county statistical yearbooks. Through Pearson correlation and partial correlation analysis, the variation trend of precipitation and air temperature on vegetation NPP and the difference of precipitation and air temperature on NPP of two alpine grasslands were studied respectively. The results show that:(1) from 2000 to 2017, the annual average temperature in Three-River Headwaters Region alpine meadow and Ali alpine steppe increased at 0.085℃/a and 0.084℃/a, and the annual average precipitation increased at 3.87 mm and 2.23 mm, respectively. The warming and wetness rate in the alpine meadow was faster than that in the alpine steppe. (2) The NPP of the alpine meadow in the Three-River Headwaters Region and the alpine steppe in Ali showed a decreasing spatial pattern from southeast to northwest. From 2000 to 2017, the NPP of 57.7% of alpine meadow vegetation presented an upward trend, while that of 50.96% of alpine steppe vegetation showed an upward trend. The NPP of alpine meadow vegetation increased more obviously than that of alpine steppe. (3) The alpine meadow in the Three-River Headwaters Region and the alpine steppe in Ali region were less affected by grazing and more affected by climate change. (4) The NPP growth of most alpine meadow vegetation in the Three-River Headwaters Region was significantly positively correlated with air temperature and negatively correlated with precipitation. The NPP of alpine meadow vegetation was mainly regulated by temperature, while the NPP of alpine steppe vegetation in the Ali region was controlled by both precipitation and temperature.