Abstract: Shifosi Reservoir locates on the main stream of Liaohe River,and has important ecological function.Taking Shifosi Reservoir as the research object,based on the two-dimensional hydrodynamic module and hydro-ecological module of MIKE21 software,we simulated the physical,chemical and biological reactions in the reservoir ecosystem to provide scientific references to its environmental management.Firstly,the parameter calibration and model verification were carried out by using the measured data.The results showed that the parameter setting was reasonable and the errors met the accuracy requirements.Secondly,the hydrodynamic model was used to simulate and analyze the hydrodynamic conditions under the flood season and non-flood season.Based on the hydrodynamic conditions of the reservoir,we simulated the degradation and migration diffusion processes of dissolved oxygen,ammonia nitrogen,five-day biochemical oxygen demand,chemical oxygen demand,total nitrogen and total phosphorus.The results showed that the inflow quantity was the main factor affecting the hydrodynamics of the reservoir,the water body in the reservoir area had good fluidity,without re-circulation area,which was conductive to the exchange of water body and the removal of pollutants.The Liaohe River flowed through the reservoir and was purified step by step,and the purification effect in flood season was better than the non-flood season.