Abstract: Restricted by topographic and route conditions,some bridges have to be constructed across the river channels by the way of skew,which results in greater resistance effects on the pier.The original text adopts two ways of empirical formula and numerical simulation to analyze the impact of the skew bridge on the floods.The backwater height and range in different flood conditions and the scour depth of the general scour and local scour are confirmed,and the water-blocking ratio of the bridge to the over-current section is also analyzed.The analysis of the backwater height,range and bridge scour shows bridge design meets the requirements basically,and the river regime doesn′t change much after bridge construction;but the water-blocking ratio of the over-current section is too large.The proposed bridge uses on-the-hole layout with the existing bridge,which has little effect on the over-current and regime of the proposed bridge,and can reduce the flood retarding effect of the two bridges.The author proposes excavation of the beach to compensate the flood area occupied by the project.By calculation and analysis of the program,it can reduce the water-blocking ratio and the backwater height effectively,and mitigate local scour,which is conducive to regional flood control.