Based on the measured hydrological data before and after the implementation of the Luocheng shoal defending project,we analyze its impact on the hydrodynamic conditions and split ratio at Kouanzhi channel upper shallow area.The result shows that after implementation of the Luocheng shoal defending project,the mainstream of Sanyiqiao shallow area has a tendency of concentrating to the center of the channel,which is favorable for the scouring of the main branch’s deep channel and improvement of the channel condition.But both the flow speed and the diversion ratio at the right branch increase,which are unfavorable for further improvement of channel condition at the left branch.