Abstract: The waterway-adaptive ship domain is used to quantitatively evaluate the conflict between ships.The quantitative Index of conflict severity degree is defined according to the proximity between ships in terms of time and space and the difference of conflict perception between ships of different sizes.The directed graph network is composed according to the conflict relationship among ships.The critical ship(as a nod) is decided through analyzing the conflict attribute, network topology and the participation degree of nods.The situation evaluation method is verified with a multi-ship encounter situation in a confined waterway in Zhoushan, Zhejiang.