Abstract: Usually in the plain a river which has separated into a number of entwined channels called the plain river network areas, where the flow concentration region is a common occurrence. Hydrodynamic characteristics of flow structure in the level crossing entrance area (i.e. +-shaped river confluence) are very complex due to common impacts given by crossing river channels. In this study, model tests on the hydrodynamic characteristics of the flow structure have been carried out and the law of variation under different boundary conditions is investigated， taking the level crossing entrance, where the Sanshan port-Wujin port is located at the Xingou River across the Beijing-Hangzhou Grand Canal, as a study example. Affected by suction flow of the Sanshan port, the current obviously flows towards the left side and flows into the Sanshan port during the inflow from the Beijing-Hangzhou Grand Canal to the Sanshan port entrance area, which results in a transverse-current area with in a certain range; affected by the Wujin port outflow′s backwater effect, the reverse current zone with a larger range appears along the right side of the Grand Canal located on the upstream outlet of the Wujin port, and the range of the reverse current zone decreases with the decrease of flow velocity from the Wujin port. The river channel boundaries have significant impacts upon the hydrodynamic characteristics of the entrance area and the change in the boundary conditions of the larger side where flow velocity is higher, which has the most obvious impacts upon the hydrodynamic characteristics. In the similar level crossing entrance area, regulation of the boundary conditions of the larger side where flow velocity is higher should taken into account when the velocity distribution is in need of change, especially for the boundary with larger flow velocity.