The Jiang’an second Yangtze River highway bridge under planning in Sichuan is adopted the diamond-shaped tandem-ranged cylindrical piers as its main towers. In order to study the influence on the navigable waterpower of the river reach under this bridge by the main tower piers,we built a 2D mathematical model for the flow to simulate the flow field before and after the scheme is implemented,and analyze the influence on the flow condition of this river reach by the tandem-ranged cylindrical piers from the view of engineering application.By analyzing the results of the mathematic model,we find that under different levels of flow,the changes of the water level and velocity in the river reach under the bridge are small,and the transverse flow velocity on the axis of the bridge is very slow,and the influence on the navigation flow condition by the construction of bridge is also small and will not affect the ship safely passing through the bridge area.