This paper expounds systematically the Quaternary geological and geomorphic characteristics of the plain along the Hangzhou Bay, and briefly analyses the transitional history and evolving trend of the coast line of Qiantang River and Hangzhou Bay. This paper then points out that a series of environmental problems that follow the continuous sea level rise will be the main threat to the coastal zone of Hangzhou Bay, and at the end, several suggestions are proposed for the urbanization planning in Circum-Hangzhou Bay.