In port and its approach channel, traffic accidents such as collision, aground, minor collision have reached about 77% of total marine casualty in the area. In this paper, an attempt to enhance the safe navigation was proposed by offering marine traffic supporting system which helps VTS operator assist vessel effectively with the quantitative assessment on difficulty of each vessel. The system collects navigation data from onboard AIS, assesses the data in assessment mode to analyze the navigation difficulties of each vessel and displays the degree of danger of each vessel on the ECDIS in real-time to decide the intervention time or order of priority for VTS operator. The effectiveness of the system was verified by the VTS operators in Korea.