Abstract: Flood merging into the Yellow River from the Xiliugou river, one of the ten major tributaries, has been simulated and analyzed in this study using a 2-D water and sediment mathematical model. Results show that the merging of hyper-concentrated flood can cause a certain rise in water level in the backwater zone upstream of the merging location along with a decrease followed by an increase in flow velocity. Increasing in flow velocity at different locations is unsynchronized. A high velocity zone occurs near the tributary mouth where riverbed has an abrupt drop, and starting from this zone, flow velocity decreases rapidly and sediment deposits in the Yellow main channel. The recirculation zone created by the merging is narrower and longer than that by low-sediment flood, and the corresponding flow structure is more complex. In the main channel, all the sediment injected from a low-sediment tributary can be transported downstream while one part of the sediment from a hyper-concentration tributary will be transported upstream. Near the tributary mouth, an upper sandbar and lower sandbar develop in the main channel. The upper bar develops from the banks to the center and finally closes up, forming a blockage. The whole lower bar rises continuously at a roughly constant rate on its left side but a gradually decreasing rate on its right side, and at the final stage it extends downstream along the right bank. Generally, velocity field and riverbed deformation around a flood merging confluence should also be closely related to the time process of floods.