Abstract: Two mathematical models by using a MIKE21 flow model with a physical model are both established to simulate the flow field of the confluence near Sanligeng reach. Because of good correspondence of simulating results and test data in comparison with each other， the establishment of the two models are both proved to be successful. Hydraulic research results given by the mathematical model show that shear force， impact force and circulation flow in the deep pool are the largest along the groove. The sediment which is disintegrated and washed down from the deep pool will bring about lateral moving because of the transverse circulation. So the sediment of the deep pool near the concave bank will be scoured and deposited in the high beach of the convex bank.In addition， through observation of the flow patterns in the physical model， it is found that the flow often changes in the form of meeting and bifurcating in the deep pool, which leads to adverse flow patterns such as vortex， flow and turbulent flow. The adverse flow patterns can improve the flow turbulence energy and carrying capacity which will provide favorable conditions for the development of the deep pool. The studies of the hydrodynamic condition in the confluence segment of Sanligeng by two models provide a theoretical basis for the regulation of the deep pool in the reach.