With regard to the coupled phenomenon of quantity and quality of lake water resources, from their coupled states, the Copula function based on quantity and quality of water is established by introducing the theory of joint probability distribution, and the inherent coupled state of quantity and quality of basin water resources is revealed. On this basis, the simulation framework of future situation is put forward based on IPCC. The researches on structural optimization of water use in Taihu Lake basin are carried out from macro view using the theory of decision-making tree. The following strategies are proposed: (1)Backward enterprises should be shut down step by step, and the optimization strategy for industrial water should be established by means of circular economy to realize industrial upgrade. (2)The strategy of farm water to realize organic agriculture is achieved by adopting new pattern of breeding and raising price of farm products to promote scientific production method. (3)The strategy of domestic water should be realized from the low-carbon life, multiple uses of water and gradually changed lifestyles.