This paper outlines the design, construction and quality assurance measures of the frame beams of the prestressed concrete with unbonded tendons in port engineering, especially the anti-corrosion measures for the ends of prestressed structure, deals with technical difficulties of water construction on large-span continuous prestressed concrete structure by the construction technology of sectional precasting and sectional tensioning. Anti-corrosion measures such as bonded tendons are used for guaranteeing the structural safety of the ends of beams.