| Tibetan Plateau,which has known as the"Roof of the World"is the largest"water tower"in the world. It is the birthplace of many major rivers in Asia, and the treasure trove of biological diversity plateau. It is one of the most sensitive areas where is response to the global climate change. Because of the specific physical geography in Tibetan Plateau, the ecological system is very fragile. In recent years, the damage codition of the Plateau's ecological environment has gone to be worse. How to maintain and protect the Tibetan Plateau's ecological balance and sustainable ultilization of resources has become an important topic all around world.Wetland is an important ecosystem which owns important ecological value. Meanwhile, the wetland developed in Tibetan plateau is the unique one in the world. It is meaningful for plateau environment. The study on the variety of the plateau wetland ecosystem and the rule how the wetland is reponse to the change of natural condition and human activities is a significant science topic.Small watershed is a unit which includes natural and human factors. The factors'exchange between material, energy and information led the small watershed to be a whole on from upstream to downstream. The proportion of Tibetan Plateau is length and breadth, the terrain is complexness, different factors make various effect. Thus,useing the small watershed as the basic research unit can make us understand the basic influnencing factors of wetland changes, explore the Tibetan Plateau's variety regular from local to overall.In this paper, the TM data in the 1990s, the ETM data in 2000s and the CBERS data in 2006s are used as the remote sensing data source to get the wetland information by human-computer interaction method. According to the ETM data, water system characteristics and physical geography, the study area is divided into 11 large watershed, and furtherly into 32 small watersheds. The study unit is small watershed. The wetland's temporal and spatial dynamic change and landscape variety are analyzed in order to realize the rule of the wetland change. Then, the mechanisom of wetland is studied from natural and ecological factors. The natural factors include climate, terrain, frozen soil and etc. The ecological factors include population and livetock. All of above is used to analyze the wetland variety driving force.This results show that:1. At present, the area of wetland in Tibetan Plateau is 138523.52km2, taken 5 percent of the whole study area. The lake wetland's aera is 66666.52km2, have been the largest during the all types of wetland. Peat wetland's area is 4894.15km2, river wetland is 50786.00km2, and the marsh is 15645.98km2. The smallest one is man-made wetland, its area is 530.88km2.2. The whole area is 142320.73km2 in 1990 and 135118.69km2 in 2000. It is decreased first (the area is 7202.04km2) then reduced (the area is 3404.83km2), during the 20 years the whole area reduced 3797.21km2. Lake wetland has been decreasing (the area is 6048.42km2), peat wetland, river wetland and marsh is reduced first and then decreased largely (each area is 201.59km2 and 3569.35km2). Marsh is decreased first then reduced a little (the area is 1749.51km2). Man-made wetland has been increasing continuously, the total area is 229.78km2, change rate is 76.31%.3. From the perspective of different small watershed,the most obvious reduction of wetland is in Qaidam flow area,the most prominent increase of wetland is in Hoh Xil flow area and Selin Co flow area. The area of wetland decreased substantially first and increased significantly in Northwest Tibetan flow area, Hei River flow area, Yellow River upstream watershed and Nujiang River watershed, The wetland in Brahmaputra watershed increased largely first and then decreased substantially .4. In recent 20 years, the wetland patch number is 20590 then increased to 30654. The wetnland diversity is increasing. It shows that the level of the fragmention is higer and the patch link degree is lower.Landscape diversity and uniformity increased continuously, it is because that the lake wetland which has decreased continuosly is the largest one in the study area. Man-made wetland increased continuously, the difference in the proportion of all kinds of wetland decreased.5. From the perspective of various small watersheds, in recent 20 years, the patch density index of the most watersheds has showed increasing trend, but the changes of diversity index and evenness index are complicated. In Chaka Salt lake the indexs reduced largely, in Jialing River watershed decreased the indexs decreased obviously, in other watershed the indexs change a little. In small watershed which has the most significant of wetland changes, the index has continued to decrease in Selin Co flow area and Brahmaputra watershed, the index slightly increased first then reduced in Hoh Xil flow area and Qaidam flow area, the index in Jinsha River watershed and Nujiang River watershed increased first and then turn to reduce. The Index has a certain increas in the Nu River, in Jinsha watershed the index decreased slightly.6. By analyzing the impact factor of the wetland in the study area, under control of the background of uplift of Tibetan Plateau, the terrain and climate condition have been made. The wetland is developing in the condition which is metioned above. In recent 20years, the air temperature has a general increasing in study area, and the precipitation has a little increasing, the glaciers has continuously shrinking, the frozen soil in the central Plateau has growing thick but thinner in the marginal areas. The amount of population and livestock has increased. Based on the interaction of these factors, the wetland in the study area has a trend of flinch.7. Base on the comprehensive analysis on the variety mechanism of the wetland, then taken Qaidam flow area, Selin Co flow area, Jinsha River and Shiyang River watershed as typical regions, it is shown that different watershed has different effect drving force, but the climate changing is the most important elements for the change of the wetland in study area. The watershed in the study area which is depends mainly on the glacier has a remarkable effect in atrophy degradation. Human activities have great impact on wetlands. Its effect is greater in the eastern area than that in the Midwest area.
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