Due to limited factors such as existing buildings,land use index,anchorage-free land in outer rivers and bridge-crossing in inland rivers,the layout conditions for the second lock project of western Dazhi River are relatively complex.Considering the factors of flow condition,navigation condition of ship lock,particularity of design ship type,berthing conditions,safety of adjacent buildings and construction conditions comprehensive,this paper determines the reasonable layout scheme of lateral and longitudinal axes of ship lock,obtains the appropriate design dimensions of lock head,lock chamber and approach channel,arranges the internal and external approaching channels asymmetrically,avoids the influence on navigation safety of ship lock when the controlling lock diverts and discharges,satisfies the mooring demand of ships getting in and out of the lock without anchorage in outer river,and achieves the goals of saving land and reducing construction impacts.