Using the Community Atmosphere Model coupling with Common land model, combined with the scope and intensity of vegetation degradation in the Tibetan Plateau, the simulations on vegetation degradation is performed by changing leaf area index in the Tibetan Plateau (27°-40°N, 75°-100°E). We discuss effects of vegetation degradation in Tibetan plateau on atmospheric circulation over the Tibetan Plateau and adjacent areas. The results show that the model can well simulate the averaged characteristics in summer geopotential heights and South Asia high position and strength, and it also has a strong ability to simulate the surface temperature field in the Tibetan Plateau, however, the center of South Asia high is too large and slightly West back. After the vegetation degradation in the Tibetan Plateau, the soil temperature and 2 m air temperature rises, surface sensible heat flux increases, however, surface latent heat flux decreases, both of which changes Bowen ratio in Tibetan Plateau. Increase of the surface sensible heat flux leads to the decrease of the 500 hPa height and increase of the 200 hPa height, which results in strong anticyclonic anomalies over 200 hPa, that makes strong South Asia high and expansion to the north and the east. The increase of surface sensible heat flux due to vegetation degradation can lead to enhanced ascending motion over southern Plateau and weakened descending motion over northern Plateau, and the ranges of descending motion exhibits northward expansion over outside of the Tibetan Plateau with weakening intensity, it finally contributes to the expansion of drying climate but with weakening drought.