In order to effectively ensure the urban water safety and reduce the carrying risk of water resources in the process of economic and social development, based on the dynamic feedback mechanism between the socio-economic system and the water resource system, a dynamic model for “water resources-social economy-ecological environment” system considering the constraints of water supply and sewage discharge is established. By selecting the coordinated development degree as the early warning index, an alarm determination method comprehensively considering the predicted value of the early warning index and the change trend of the index in the next year is proposed. Taking Nantong as the research object, the results show that the current development mode has achieved good results in the early stage. However, with the elapse of time, the carrying status of water resources will be upgraded from level Ⅳ to level Ⅲ, it will be getting worse, and the development direction needs to be adjusted in time. In the future, the water use efficiency should be further improved and the governance of point source pollution and non-point source pollution should be strengthened in Nantong City.