Abstract: The cathodic protection system is important for ensuring safety of floating production storage and offloading (FPSO) hull structure. Taking the cathodic protection system of a deep water FPSO hull as an example, the technical requirements of cathodic protection system using sacrificial anode for offshore floating units was introduced in the oil company's general specifications. The general design of the FPSO incorporated the concept that the oil tank section was embraced and protected by a "dry safety belt" for reducing the consumption of anodes in FPSO tank. The composition and size of aluminum alloy sacrificial anode were selected considering the influence of corrosion environment, cathodic polarization process, consumption of sacrificial anode, breakdown of coating and limited arrangement space in tank based on the DNV rules and oil company's general specifications. In order to meet the design requirement of FPSO hull without dock maintenance during it whole life of 28 a, the protection current density required by FPSO hull and underwater hanging facilities was calculated to determine the amount and arrangement of sacrificial anodes in the FPSO tank and outboard shell.