Analysis of the vegetation coverage changing with the time in the last 21 years is the purpose of this paper to study the regularity of the regional eco-environment in the Tibetan plateau. Based on the remote sensing data GIMMS NDVI, statistical processing and analysis, also calculation, the paper gives quantitative analyses and evaluations of the variability of vegetated rate of the Tibetan plateau. In the last 21 years, the regional vegetation coverage has been on the slow increase at the rate of 3 961.9 km2/a as a whole, except for some place degradation, and also the human have not done damage to the eco-environment. From 1982 to 1991, the vegetation coverage of the whole region increased, except for degrading region at the middle and the west of the area. The value increased is decreasing from the south and the east to the north and the west. The induction, the climate benefiting the vegetation growing, changing with degree of longitude and latitude, can be worked out. It's the main period from 1992 to 2002 that the vegetation degrade, those deteriorated regions are located in the resource regions of the Yangtze river, the Yellow river, the Lancangjiang river and the Nujiang river, which indicates the changing climate would be adverse to the vegetation. The NDVI also has two significant periods of 7 years and 3.5 years, caused by the same significant periods of the temperature, and that indicates that the plateau plant is more senstive to the temperature than to the precipitation. Over 21 years, there are 7 from 8 types vegetation coverage which are raising unstably including clod-arid-region plant with vulnerability and difficult recovery.