Objective The position of the structure where the electric current flows into and several other problems were studied in the designing process of impressed current cathodic protection for offshore jacket, and the achievement could offer a reference for cathodic protection of platform offshore jackets. Methods In this paper, several problems in the design of impressed current cathodic protection for offshore jacket, including protected objects, power point, the selection of auxiliary anode, the number and the location of auxiliary anode, were studied by the numerical simulation software, BEASY CP. Results If only considering the part of offshore jacket surrounded by seawater, the structure could not be protected effectively by the impressed current cathodic protection system. The protective potential of the two design schemes including and excluding resistance (1.01×10-6 Ω/m) was close to each other and the absolute error was less than 1 mV. The protective potential was less affected by the setting of power point. The distribution of protective potential with three different diameters of auxiliary anode, 300 mm, 600 mm and 900 mm, were all in the range of 803~899.2 mV (vs. CSE). The protective potential of three anode design schemes with 17 A, 17 A and 16.5 A output current respectively, were 803.34~899.20 mV (vs. CSE), 802.96~850.64mV (vs. CSE) and 800.36~848.26 mV (vs. CSE), respectively. It can be seen that the protective effect of 2# anode scheme was better than 1# anode scheme, and the anode scheme with two anodes was the best. Conclusion All metal structures should be considered in the designing process of the impressed current cathodic protection system for offshore jacket. For small jacket, the protective potential was less affected by metal resistance, so the power point was easy to determine. It was important to consider the influence of current density on anode consumption and select the suitable anode size in the process of cathodic protection system design. The number and setting location could be optimized by numerical simulation method in order to obtain a better protective effect and reduce the requirement of protective current.