Based on the data collected from the river closure reach and the open diversion channel and the closure gaps located the up and downstream cofferdams, including water level, flow velocity, river bed topography and water surface flow region, the variation law of the hydraulic factors on the reach (especially at the closure gaps) and the relationship among themselves are analyzed in this paper. The results show that the flow velocity at the longitudinal and horizontal cross-section are affected by the closure dike and bed filling constructions as well as condition of the inflow and sediment. The observing seepage inside the cofferdam would be helpful to research the diversion rate of the open channel and stabilization of the closure dike made of rock chunk.