Abstract: Based on the experimental results of river model and measured data of related bridges,variations of discharge and sediment movement in the bridge reach after bridge building are analyzed,and influences on bottomland are discussed.Results show that after the bridge building,the water level,velocity,flow direction and unit discharge in the reach near the bridge have changed,i.e.the closer to the bridge,the bigger the influence,and that different bridge types have different effects on the bottomland.For the bridge with a big main span and dense piers in side spans,which is usually adopted at present,it is easy to form new side bottomland or cause the existing side bottomland to become bigger and higher.