Abstract: Apron pipelines are easily blocked by the corrosion products which are generated by the water accumulated at low positions of the pipelines, so their normal operation is impacted. In this paper, 3D numerical simulation was performed on the flow characteristics during the expelling of water accumulated in apron pipelines by using CFD technology based on the computational fluid dynamics (CFD) and the principle of equivalent shear stress. Then, the expelling situations of the water accumulated at the low positions of apron pipelines in the working conditions of large pipe diameter were analyzed. And consequently, the main parameters influencing the flow pattern of water accumulated in the pipeline and the critical condition of complete water expelling were figured out, and the flow characteristics of the system after the accumulation of water in apron pipelines were revealed. It is indicated that the forms of the water accumulated at the low positions of pipeline are related with the oil flow rate, pipeline arrangement and water content. In order to carry the water accumulated at the low positions of pipeline completely out of the pipeline by using the oil inside the pipeline, it is necessary to increase the oil flow rate, reduce the dip angle, and decrease the water content. The study on the flow characteristics of water accumulated in large-diameter pipelines is of instructive significance to the actual expelling of water accumulated in apron pipelines.