The pollutant degradation coefficient is one of the key parameters to describe the water quality change, for establishing a reasonable water quality model and to determine the water carrying capacity and the environmental capacity. In this research, the environmental channel experiment is conducted to simulate the degradation evolution of the COD and NH3-N under different flow velocity conditions in typical pollution water. It is shown that the processes of the COD and the NH3-N’s concentration over time are quite consistent with the first-order kinetic equation and the degradation coefficients increase with the increase of the flow velocity. When the flow velocity varies from 0 m?s?1 to 0.87 m?s?1, the degradation coefficients of the COD and NH3-N increase from 0.011 d?1 to 0.071 d?1 and 0.038 d?1 to 0.258 d?1, respectively. Moreover, the COD and NH3-N’s degradation coefficients both have excellent correlation with the reaction time. There is a good linear relationship between the COD degradation coefficient and the flow velocity as well as a good power exponential function between the NH3-N degradation coefficient and the flow velocity. The compa- rative analysis of the Youth canal prototype monitoring and the calculation results shows that the quantitative formula obtained from the indoor water channel experiments gives results very close to the prototype observation results, which could reflect the degra- dation of pollutants in river water with varying flow velocity.