The study focused on the water quantity exchanges between the typical river network area (at Dapu Town, Yixing City) and the western Lake Taihu. Effect of rainfall taken into consideration, the runoff formation and flow concentration model considering various underlying surfaces was adopted to simulate the runoff process, both of the typical river network area and the nearby western hill area(2002 (base year), 1998 (wet year), 1995 (normal year) and 1994(dry year) respectively). Then the non-steady stale river network water quantity model was established by adapting to the typical river network area. Combined with the results of the runoff formation and flow concentration simulation, the water quantity model was applied to simulate the dynamic changes of water flow in the typical river network area, for each year mentioned respectively. Finally, water quantity exchanges between the typical river network area and the western Lake Taihu was ascertained. Changes of the water quantity exchanges in the year and between the years was also studied, on both co-current and adverse current conditions.