Under the interval uncertainties, by incorporating the discretization form of finite volume method and interval algebra theory, an Interval Finite Volume Method (IFVM) was developed to solve water quality simulation issues for two-dimensional river when lacking effective data of flow velocity and flow quantity. The IFVM was practically applied to a segment of the Xiangjiang River because the Project of Hunan Inland Waterway Multipurpose must be started working after the environmental impact assessment for it. The simulation results suggest that there exist rather apparent pollution zones of BOD5 downstream the Dongqiaogang discharger and that of COD downstream Xiaoxiangjie discharger, but the pollution sources have no impact on the safety of the three water plants located in this river segment. Although the developed IFVM is to be perfected, it is still a powerful tool under interval uncertainties for water environmental impact assessment, risk analysis, and water quality planning, etc. besides water quality simulation studied in this paper.