This paper discusses the calculation of current and potential distribution of cathodic protection models with nonlinear polarization curves. We use the Newton-Raphson iterative method for the nonlinear problem and present some interesting feature that the iterative sequence is monotonically convergent for arbitrary initial guess when the polarization curve is convex. This feature is of significant importance in developing a computer code for the design of cathodic protection systems. Also, an algorithm is proposed for problems with nonconvex polarization curves. Boundary element methods are employed for the numerical calculation.