The flux-current characteristic curve of electromagnetic PT is usually obtained by estimating the fitting parameters based on the Least Square method and experimental characteristic data. When the equation set is solved with traditional Newton method, the Jacobian matrix has a larger scale and is badly affected by the initial value of fitting parameters due to large amount of experimental data. The iteration is probably not convergent. A comprehensive fitting parameters’ solving method based on the combination of the general polynomial and orthogonal function system is presented. This method makes the scale of Jacobian matrix downsized and confined by the number of fitting parameters rather than that of experimental data. Therefore, the calculation efficiency is enhanced and the convergence of iteration is guaranteed. And the whole computational process is more stable. Simulation verifies that this method can simplify the overall calculation and has higher fitting accuracy. In case of large amount of experimental data, the superiority of this method can be better projected.