Abstract: In the light of the real conditions of Inner Mongolia reach of the Yellow River, a mathematical model is established based on the case of the flood variation, tributaries, and insufficient hydrologic monitoring stations. The confluence analysis and calculation results show that the numerical model can truely reflect the flow regime in the Inner Mongolia river reach from the tributaries and the related changes in hydraulic elements, which can be used as one of the research methods for regalation of this river reach. The large inflow discharge from the tributaries in Inner Mongolia into the mainstream of the Yellow River can give considerable influence on the flow regime and water level in the mainstream zone, and result in changes in flow direction, water flow over the beach, rise of stage, so those problems concerned should be paid much attention to and be taken into account in the regional flood control planning and river regulation. Considering the tributary inflow into the mainstream of the Yellow River in the Inner Mongolia reach has impacts not only on the flow pattern, but also on river channel process, it is difficult to simulate the flow process of high sediment concentration within a short period, so the next step is to simulate the process of sediment-laden flow on the basis of the existing flow.