The east Taihu Lake which have the functions of flood control, water supply, water environment protection and aquiculture is the representative grasslike lake in the middle and lower reaches of Changjiang River, it is also the main water exit and adlittoral arm of lake of Taihu Lake and the main water resources of Shanghai City, Jiachenghu town of Zhejiang Province and Wujiang City of Jiangsu Province. For almost half a century the surface of east Taihu Lake constantly reduced by the long-term effect of the natural and artificial factors. The shape of lake and the water environment were seriously damaged which made the process of lake's decay become more faster and cramped the functions of discharge, water supply and water environment protection. This article reviewed the evolution of east Taihu Lake and initially discussed the actuality and effect on the lake's function of the shrinking of surface of east Taihu Lake. And also, several suggestions were carried out for reference on the present treatment plans of the lake.