With the completion of the Qitai operation area and the auxiliary breakwater project,Lianyungang port has become a long narrow semi-enclosed harbor region.As the entrance of the port becomes narrow and the distance from the entrance to port ends increases,the exchange capacity of the harbor water will certainly be affected.In this article,the water exchange capacity before and after the engineering is studied using a three-dimensional mathematical model and further understanding of the exchange process in the harbor waters is carried out by Lagrange trajectory method.The simulation results indicates that under the impacts of flow dynamics and the port shape,the half exchange period increases from about 5 days to 22 days after the construction of Qitai operation area and the auxiliary breakwater project.In order to guarantee the water quality in the port,the amounts of wastewater discharged into the port must be controlled strictly.