Abstract: During the trade transaction of offshore crude oil, the accuracy of transaction data is closely related to the interests of both buyers and sellers. If the deviation between the measured data of ship and the FPSO flowmeter is more than 3‰, the consignee may raise a claim or reject to accept it, and thus, a dispute is produced. Hence, the anomalies during the outward transportation of crude oil by FPSO in Bohai Sea in recent 5 years were analyzed and studied, and five factors influencing the measuring accuracy of crude oil transported by FPSO were put forward with reference to the relevant standards and experience, including the human factor, equipment factor, oil variety, measuring method and environment. Through systematic analysis on these five factors, the key control points affecting the outward transportation measurement were found out easily, and the methods for reducing or eliminating these anomalies were studied. The results show that the measurement error could be effectively reduced by perfecting the relevant operation standards and procedures to ensure the operation more standard and reasonable.