The object of research is Chaping River which flows over Anxian County in Mianyang City, Sichuan Province. Based on agreat number of investigations on the load of water pollutants, the situation and function of water environment of the river, theriver-basin hydrological character, the river draining plan, and observation date at environmental monitoring station of MianyangCity Sichuan Province in 2005, two-dimensional hydrodynamic shallow-water model equations were used for monitoring COD and NH₃-N concentrations in section of the Chaping River and the simulations were compared. A one-dimensional model was used tocalculate the water volume capacity of the river's water environments and the ways controlling the total quantity were provided.Results indicated that using two-dimensional hydrodynamic shallow-water model equations to calculate the monitoring sectionshowed a small measured difference for COD and NH₃-N. For the water environmental capacity of Chaping River, COD was 123.96t/a and NH₃-N 42.95 t/a. The COD and NH₃-N emission volume would exceed the capacity in the basin, and the quality of outputwater would exceed the III grades of water protecting standards.