| Cultural eutrophication is the primary problem facing most surface waters today, most of lakes in China is in the danger of catastrophic shifting in ecosystems. To restore or reestablish aquatic vegetation is the key to restore the intact lake ecosystem. We haven't, however, know enough about the environmental factors or ecosystem process, which driving and influencing the decline of aquatic vegetation, let alone to use these knowledge to reserve and restore the systems. Differences in the natural distribution of aquatic plant species are related to plant growth form and determined by differing physiological abilities to exploit the environments. To find out the key driver and the related mechanism in the succession of aquatic vegetation, the present state and long-term changes in the aquatic vegetation in Dianshan Lake was studied, combined with the changes in environmental influences and plant traits of dominant species. The trend of succession was also discussed. The results indicated that:(1) Since 1959, there have been 41 species, which bleng to 34 genera,24 families, found in Dianshan Lake. During the lates 51years there have been 12 species disappeared and 10 species new occoured, with the proportion of cultivated or exotic species becoming higher than in the past. In the lates 33 years the aquatic vegetation decline dramatically in Dianshan Lake, with rooted macrophytes communities lost more than 90% while communities dominant by free-floating and exotic or cultivated species increased to be over 90% of the vegetation now. During the same period, the life form and growth form of dominant species shifted to larger and higher turnover rate ones, which were more adaptive under the high level of nutrient and disturbance. Phytoplankton have become the primary producer in Dianshan Lake, indicating that the whole system had switched to the turbid state which dominated by phytoplankton.(2) Differences in the natural distribution and abundance of aquatic plant species are close related to plant growth form and determined by differing physiological abilities to exploit the environmental resources. Magnopotamids plants Potamogeton malaianus could establish communities in large water, for its high tissue intensity. Parvopotamids plants Hydrilla verticillata, which were characteristic of small leaf, high SLA and SLA for shoot combined with locating most leaf in higher water layer, were capable to exclude other species and form density plant beds in small water. The decline and vanishing of communities of Vallisnerids plants Vallisneria natans was most due to the traits of large leaf and locating most leafs at the bottom of water; Species capable to survive in eutrophic waters all had the traits of small leaves (high turnover rate to grow fast to break the light limits in the bottom water) and locating most leaves in higher water layer(for photosynthetic tissue to get most light). These results suggested the mount of light avalability was the key to drive submerged vegetation succession.(3) Depth of euphotic zone in Dianshan Lake varied in different seanons, Deu in winter was much deeper than in spring and summer. From north to south part of Dianshan Lake, Deu grow gradually, with the value of influences of it diclining with some fluctuation for the different types of habitat, water terbulence induced by human and wind in summer. Deu was most regulated by content of SS, flowed by Chla, with the explained rate of 33.8%, the low rate of explaintion may be due to the high wave which reflecing large part of light. Deu/H lower than one in spring and high water level in summer si the key environmental factors to hinder the vegetation recovery. In order to reestablish aquatic vegetation, the Deu/H should 1, which means that the Secchi depth should be fit the equation SD>0.313H-0.107.
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