Research on city eco-security early warning based on System Dynamics — A case of Liaohe River

City eco-security early-warning evaluation indicator system of Liaohe River watershed based on Pressure-State-Response (P-S-R) was established, and on the basis of which, city eco-security early-warning model of resources population economy society environment composite system was built in this paper. This research adopts a combination assessment methods, simulates a series of eco-security early-warning indexes of Liaoning Province from 2010 to 2020 through VENSIM, to evaluate eco-security early-warning index value of 15 cities.The results show that eco-security early-warning assessment can be sorted into three types: safe areas, consistently endangered areas and degraded areas. The latter two is regarded as early-warning areas, its eco-security trend is very serious in future ten years. The simulation results show that the model based on SD of the eco-security early-warning agrees with actual state. The results provide a theoretical basis for the development of Liaohe River watershed plans.