The wide gradual reach is a common form of natural rivers because of the impacts of flow and sediment conditions, and man-made projects.Based on the flood process and erosion and deposition of hydrological observational cross section in a gradual width river, the hydrodynamic characteristics was simulated and analyzed by means of a two-dimensional flow model. The comparison between observation and simulation showed that the intensities of increase and decrease of flood depend on the value and duration of flood process, and the velocity distribution at any cross section often change with the variation of asymmetry river wide, which affects the bed deformation in the whole reach considering the effect of sediment critical incipient velocity.
