Hydraulic and sediment balance and boundary conditions of the lower Yellow River have changed significantly after Xiaolangdi Reservoir had been constructed.Under the changed scenario, the river bed and river regime in the downstream river course would appear new evolution trends.The paper took the consecutive meandering reaches between Weinali and Datianlou of the lower Yellow River as the case study,and used mathematical model Delft3D to simulate the flow patterns in meandering streams under the changing hydraulic and sediment conditions.Results show that the depth-averaged velocity changes significantly along the longitudinal and transverse direction, and the flow pattern is not the same in different parts of the curved reach as it was before. In addition, the existence of the marginal bank and the deep groove further exacerbates the inhomogeneity of velocity distribution and redistribute the flow velocity. And the flow dynamic axis is closely related to the different scales of the flow discharge, when the flow discharge is higher or lower, the variation of mainstream line is different, which has a significance influence on river bed evolution.