This article reports protection technology against damages to seawater refrigerating system and to seawater transporting pipeline, caused by seawater corrosion and marine biological filth. Two methods, seawater electrolysis method to prevent biological adhesion and applied current cathodic protection method to prevent corrosion by seawater, were cooperatively applied to the system under protection. These new technology and apparatus against corrosion by seawater and adhesion by biological filth were used to develop a monitoring, automatic corrosion control, and alarm system which not only solve the corrosion problem in the installation, transportation setup and seawater delivery pipe in the sea, but also provide monitoring, control and early warning alarm to the status of the protection system to ensure the safety of production. The principles and applications of the dual-protection system technology are also discussed.