Wetland is the conjunction of lake and terrene and has important ecology function. Through the studies on the distribution of chemical elements and the diatom assemblages in longgan Lake sediments,we have found that the wetland has obviously buffer function to the materials form land to lake and is effective to keep a good lake ecology. Human activities have destroyed the wetland in the area of Longgan Lake,weaken the ecology function of wetland,and accelerated the deterioration of lake ecology.