Voyage statistics is often required in fishery management, fishing benefit calculation and resource surveys. It is used as an important reference value. Vessel monitoring system based on Beidou provides a fast and convenient means for obtaining voyage. More than fifty thousand fishing vessels had installed the terminal unit of the Beidou satellite positioning system since the Ministry of Agriculture of China started to construct fishing vessels monitoring system in Nansha Islands in 2006. The data sent by the terminal unit have a temporal resolution by 3 minutes, and a spatial resolution by 10 meters. Thus, after carrying out these fishing services for nine years, the system has recorded billions of historical cruising data for each vessel, including the time, position, speed, direction, rate of turn, etc. During the fishing operation, a complete voyage includes sailing, marine operations, and return. The ports of fishing boats sailing and return are often different. A surface was formed by the buffered land and islands with ports. Offshore distance is between ship's position and the surface. Fishing voyage is determined by the change of distance offshore. Voyages are extracted by programming. The results of six research ship voyages were compared with 43 cruises actually recorded. The difference proportion within two days of the start voyage was 95.1%. The difference proportion within two days of the end voyage was 95.2%. It can provide a more accurate reference for fisheries analysis.