Abstract: Abstract: To study the spatio-temporal variation laws of moisture index of alpine meadow in Tibet, according to the data on the average daily temperature and precipitation from 38 meteorological stations in Tibet and surroundings in 1971-2010, the authors adopted the moisture index (K) and the ArcGIS software to analyze the spatio-temporal variation laws of moisture index of alpine meadow in Tibet for nearly 40 years. The results showed that: (1) the average moisture index decreased from northeast and southwest to central Tibet, which appeared banded; (2) the variaton trends of moisture index had pronounced regional characteristics, some areas of Changdu and Rikaze had a increasing trend, conversely, other regions had a downward trend and obvious aridification; (3) the moisture index presented a trend with “increase-decrease”, resulted in the area decrease of alpine meadow from 94.61% in 1990s to 83.24% in the beginning of 21st century, this also proved that the aridification was significant in research regions; (4) the location of 1.2 contour of moisture index had a clear displacement, invaded to northeast and into alpine meadow and alpine steppes. The regions where the alpine meadow distributed should pay high attention to the drought phenomenon during the climate changing in the future.