The distribution characteristics of pollutant dispersion coefficient in the confluence of a curved river with tributary are studied. The mathematical model of air-water two-phase flow in the U-shaped confluent channel is established and verified by the data of previous laboratory experiments. Based on the simulation results, the influence of different discharge ratio on the flow structure and dispersion characteristics of confluent curved river is analyzed, in which the dispersion coefficient is calculated by the two-dimensional tensor method. The results show that the dispersion coefficient reaches the peak value in the vicinity of convergence, and the peak value increases with the increase of discharge ratio. Moreover, the longitudinal dispersion coefficient shows a single peak distribution along the river, while the transversal dispersion coefficient presents a double-peak structure.