The numerical least-square fitting is a general method for the extraction of model parameter from experimental data. However, the method suffers from an initial value dependence problem when the method is used in I - V curve fitting. Recently we have proposed a successive large perturbation method (SLPM) to eliminate the initial value dependence problem. In this paper, we test the SLPM by comparing our results with previous published fitting results for various solar cells, such as traditional silicon solar cells and new type of organic solar cells and dye-sensitized solar cells. The method is available not only to the fitting for I - V curve, but also to the fitting for electrochemical impedance spectrum. Our test demonstrates that Newton-like method plus our SLPM is an accurate and robust method for the numerical extraction of equivalent circuit parameters in solar cells.