Cathodic protection (CP) plays an important role in protecting offshore structures from corrosion. More and more numerical simulations are employed in designing and evaluating cathodic protection systems with the development of computers and numerical methods. The CP problem is governed by Laplace’s equation, and mostly simulated by boundary element method (BEM). However, BEM consumes a large amount of computer memory and is very inefficient when it is used to simulate large-scale models. The BFM is developed to simulate the CP problem. Two common potential problems are solved to validate the accuracy. The results show that BFM is more accurate than BEM. Then, the CP problems of a subsea pipeline, an hourglass type floating production storage and offloading system (FPSO) and a tension-leg platform (TLP) are simulated. The results show that BFM is more accurate than BEM and costs less time when the same precision is achieved in most cases.