Abstract: In the narrow channel,the close distance of large ships will produce the inter-ship effect,which makes the ship appear attraction,repulsion,turning and other phenomena. The safety and efficiency of navigation is affected seriously.With the development of ship upsizing,scientific and reasonable determination of the minimum encounter distance（or safe encounter distance）between large ships has not only a certain theoretical significance,but also a strong practical value,In this article,taking the Xiazhimen Channel as an example,by establishing a ship motion model and implementing simulation maneuvering,and analyzing the hydrodynamic interaction between two ships at different encounter distances,the minimum encounter distance between two ships without large deflection is calculated. By means of questionnaire survey and field observation,the safe encounter distance of large ships in the narrowest part of the Xiazhimen Channel in navigation practice is calculated. By comparing the results of theory and practice,the safe encounter distance of two ships in the Xiazhimen Channel is determined,and the reference suggestions are put forward for the encounter distance of large ships in the narrow channel,in order to reduce the risk of large ships and improve the navigation efficiency.