Abstract: Taking the Wenruitang river system as a case study,a dynamic water quality model for looping river networks is developed based on the framework of uncertainty analysis.The distribution of water quality parameters can be got by the HSY (Hornberger,Spear and Young)algorithm based on the uncertainty analysis,which can improve the credibility of the model simulation and reduce the risk of the decision making.The model consists of two sub-models,i.e,the hydrodynamic and the water-quality models.The hydrodynamic sub-model is based on the Saint Venant equations and the four-step numerical method is applied to their solutions.The water quality sub-model is estabilished from the CSTR concept,yet with essential amend ments in accordance with the requirements of looping river networks. Only ordinary differential equations need to be solved, and the matrix solving can be avoided so that the calculation efficiency is greatly improved,which makes HSY algorithm possible to be used.The model is firstly applied to Lucheng river network,which is the key part of Wenruitang river system in Wenzhou City HSY algorithm is used to calibrate the model parameters,and the parameter's uncertainty is analyzed.The model is verified and the results are relatively ideal Finally,the uncertainty transfered to the simulation results due to the parameter's uncertainty is briefly discussed.