Conflicts represent near misses between two moving vessels, and often occur in port waters due to limited sea space, high traffic movements, and complicated traffic regulations. Conflicts frequently result in congestion and safety concerns. If conflict risk can be predicted, one could take appropriate measures to re-solve conflicts so as to avoid incidents/accidents and reduce potential delays. To the best of this researcher’s knowledge, no systematic study has been carried out on the issue of detecting marine traffic conflicts. In this paper, we present an algorithm designed to determine a conflict using the criterion of vessel domain. The al-gorithm aims to evaluate the relative positions of vessel domains to detect potential conflicts. To implement the algorithm, a simulation model has been developed in Visual C++. The model at present provides a single function for conflict detection but can be expanded to a multi-functional system for resolving conflicts in fu-ture work.