Abstract: The vertical turbulent mixing process of point source and linear source in nature rivers are studied in this paper. According to the vertical turbulent mixing process near the discharge point in large rivers,the new concept of part depth of homogeneous mixing is presented.The basic equations of vertical mixing process are developed.The fundamental relationship between the part mixing depth and the vertical mixing distance is obtained.The distance of vertical homogeneous mixing in whole depth can be calculated by the theory equation,which is deduced in the paper.The equat ion is also verified by the measure data in the Yangtze River.On the base of the law,a 2-D water quality numerical model which is mixed through part depth homogeneous is developed,and used in the concentration field calculation.By use of the measure data of Rhodamine-Btracer in the Yangtze River estuary,the comparison of the value calculated with the data measured is made.The value calculated by the new model is more precise than that calculated by the traditional 2-D model,and it is more efficient than 3-D model.