Abstract: Paper focused on polders in the Yangtze River Delta. It argued that, from the landscape architecture’s ecological perspective, the underlying mechanism relies on the capacity of ecosystem services provision, and influenced by physical form. Physical form impacts the provision of ecosystem services, which can be clarified and measured. Through studying the correlation of “water-green-people”, this paper explained the formal characteristics of traditional polders and revealed their underlying 8 types of ecosystem services. It also criticized the conflicts and problems in the existing polders, and finally suggested three principles to guide future practices in polders in the delta, including the idea of “following water” and appropriate changes to nature, total human ecosystem to integrate ecology, production and life, and social governance system to coordinate with water.