As part of the coastal wetland ecosystems, mangroves thrive at the interface between land and water. The slope connecting the main river channel and floodplain has been found with different angle. The vegetation density also influence the penetration of the flow. This research studied the hydrodynamics in a partially vegetated compound channel by using the 2DH RANS model in Delft3D. The numerical model is calibrated with the results of flume experiments. The drag coefficient with a value of 0.8 and the background horizontal eddy viscosity with a value of 10-4 m2/s are suggested according to calibration of the model. The influence of different slope angle and vegetation density on flow characteristics is studied. It is concluded from the model results that a denser vegetation patch leads to stronger momentum exchange at the edge of vegetation patch. It is also found that a slope angle around 1/10, which is the most typical slope angle in Mekong estuarine system, leads to the strongest eddy structure and the largest amount of momentum transport into the vegetation patch. It implies that a slope angle around 1/10 might be the equilibrium state of topography in mangrove coast.