The numerical model,which combines the two-dimensional river model and ship maneuvering mathematical model,is built.The influence of Nanjing Fourth Bridge to be built across the Changjiang River on river's condition is studied.The change of river conditions around the Bridge pier is analyzed and the tracks of ship transit along the reach of the Changjiang River are simulated for the cases of before and after building the Nanjing Fourth Bridge.The parameters of navigation in sail course have been obtained.The result shows that the influence on rivers condition of the Nanjing Fourth Bridge on Changjiang River is very small,and its influence on navigation is not significant.