Abstract: AIS（Automatic Information System） data in October, 2019 are analyzed with quaternion ship domain to find non-accident critical events. It indicates that this kind events mostly happened at Wusong Estuary, in the South Passage and in the area of Zhoushan port, Ningbo. Statistical analysis is performed on navigational factors related to those events to find their distribution characteristics. The Closest Point of Approach calculation is also performed to find most critical 10% of NACEs. The location distributions obtained from both methods agree with each other, which proves the effectiveness of the new method.