In the Minjiang Longxikou Navigation-power Junction project,the ship lock is adjacent to the flood discharge gate,the different outer wall structural sections of the upper lock head and lock chamber lead to planar morphological mutation of the ship lock,during flood discharge,the sudden expansion area will experience severe flow patterns such as large-scale backflow and turbulence,which will affect the junction flood discharge.By establishing a planar two-dimensional mathematical model,the flow field distribution before and after the arrangement of the guide wall at the front toe of the outer wall of lock chamber is calculated,the results show that the length of the backflow is about twice the width of the sudden expansion area,and the arrangement of the guide wall according to this range could basically eliminate the backflow,the curved guide wall could make the longitudinal flow velocity contour uniformly decreasing,thus the flow patterns optimization is better.