The lowest water requirement of the wetlands was demonstrated through different simulations. Based on the relationship between the area of wetlands and its effects on air temperature and humidity, some useful statistical models were established. According to the theory and principles of system dynamics (SD), a dynamic simulation model of the wetlands' retaining water was compiled in DYNAMO language. Finally, the safety threshold of the wetlands was assessed based on its water ecological factors. The feasibility of the method was demonstrated by a case study on the wetlands in Sanjiang Plain of China.