Abstract: An unsteady water quality rmdel for looping river network is developed for water pollution control planning of the Wenruitang River basin in Wenzhou City.It is based on the Saint Venant equations and the conceptual model(the contunuously stirred tank reactor,CSTR).The rmdel is made up of the hydrological sub-rmdel and the water quality submodel.It can show the dynamic changes of COD,ammonia-nitrogen and DO in the river network.With the model,water environmental capacity of Lucheng river network is estimated.The short-term and long-term pollution control objectives are also worked out.After the study on characteristics of water quality restoration,it can be concluded that the irregular measures such as polluted watercourse flushing and aeration could be taken.Furthermore,nine scenarios on polluted watercourse flushing are analyaed quantitatively,and river reaches required aeration are screened out,too.