Abstract: In order to study the influence of hydrodynamic conditions change on the local scour of bridge foundation of complex cap pile group, the main pier foundation of Dongbao River Bridge was taken as a research object.A large-scale(1∶15)normal physical model test was carried out to study the shape and scale of local scouring pit, and the dynamic response of scouring process under different flowing angles and hydrodynamic conditions.The results showed that the scouring effect of small deflected flow on piers was generally enhanced.After the implementation of the new projects around the bridge, the water depth around the pier became smaller, the flow velocity became larger, and the influence range of the scouring pit increased.When the flow deflection angle were 0°and 5°,the maximum scouring depth increased by 17% and 16% respectively.Under the combined influence of the complex cap structure and the water-blocking effect of the pile group, the scale of the three scouring pits generated along the axis of the pier decreased in turn, and the sand ridge was deposited at the end of the scouring pit.The scouring pit changed from inverted cone to semi-elliptical shape on the elevation, and with the increasing of elevation, the increase of the horizontal size of the scouring pit slowed down, while the cross-sectional area increased significantly.The research results can provide reference for the safe operation of bridges with similar complex pier types.