The second Minjiang river bridge to be built locates 1.4 km downstream of Zhushitan,the 215 m-long main navigable hole of which locates on the right side of the channel,and the linking of which to the new groove faces a big problem.At present,the old groove is not deep enough for the passing of large transport ships.The 2-D flow sediment mathematical model is established,and the similarity is verified by the measured data.The calculating results of the water line,the velocity distribution and the river bed scour are consistent with the measured data,so the accuracy meets the specification requirements.To reach the IV channel standard and meet the need of large transport ships,we compare the schemes of old groove and new groove.The results show that the mathematical model can simulate the movement of the river flow and sediment deposition process of navigation channel.It shows that three schemes all have their own advantages and disadvantages from the regulation effect (the flow condition for navigation,navigation channel stability,etc.).Relatively speaking,the old groove scheme is better,since it can meet the requirements of the channel’s navigation condition.