A simulation-based system dynamics (SD) model was developed for allocating the waste load and supporting river quality management. Panjin section of Liaohe River in China was used as a study case to demonstrate the feasibility of the proposed methodology. The national surface-water environment function zoning of Liaoning Province was presented as a constraint in order to calculate the maximum allowable waste quantity for COD, which is expressed as interval format of both upper bound and lower bound. Then allocate the waste load to each point source responses within these quantities. The study results simulated from SD model, together with the intervals-format uncertainties of allowable COD level is valuable for supporting decision makers in optimizing water quality management.