Cathodic protection is one of the most important techniques to prevent damage caused by corroding of steel marine platforms. The development of offshore oil and gas fields and the high costs of manufacturing, launching and maintaining of marine platforms, more than ever, the importance of preventability of marine platforms corrosion has been appeared. Over the past decades, the use of numerical modeling in the design of cathodic protection systems to improve performance, increase operation period and reduce in costs has been increased significantly. In this study, the results obtained from sacrificial anode cathodic protection system modeling of steel marine platform in the Persian Gulf and the Caspian Sea have been reported. Zinc anodes were used. COMSOL Multiphysics 4.2a software was used for modeling. The relationship between the potential and cathodic/anodic current density obtained from potentiodynamic measurements were used as boundary conditions. The optimum design for the cathodic protection system was determined. The anodes were roughly uniformly distributed on support tubes in optimum design. The potential distribution over the platform surface and also mass loss rate of the anodes in this design were uniform. The highest and the lowest mean current outputs of anodes in optimum design are 113 and 93 mA. The SA system produced the highest current density output for the anodes and protective current density over the platform. To validate the modeling results, the potential values of a physical platform model was measured in Caspian Sea. The maximum relative error of results was 7%. However, there was a good agreement between the results obtained by FEM model and measurements. Keywords : Cathodic protection, Modeling, Finite element, Marine platform, Potential, Current density