Abstract: The influencing factors of risks that associated with piloting a ship in port are analyzed and their unascertained measurement model of the factors are identified. Copula function is used to weigh the risk factors and a risk assessment model involving the factors with uncertainty is built. Particularly, the process of piloting a ship through the Pearl River Estuary is quantitatively studied through analyzing several scenarios. Relatively significant situation features of pilotage operation are identified and risk assessment is conducted. The results are examined against practical pilotage processes and proved. The research shows that the risk level in middle-late stages of piloting a ship through the pearl river estuary is medium and tide is the critical factor influencing the risk situation.