Abstract: For the widely used crystalline silicon photovoltaic（PV）modules,an accurate simulation model with double diodes of the solar cells is established on Simulink. The most common partial shading faults of PV modules in practical applications are simulated and verified under various working conditions. According to the characteristics of the inflection point,step and the integral area（S）based on the I-V curve,an online partial shading faults diagnosis method of PV modules using the characteristic of S-V curve is proposed. This method establishes the S-V curve of the PV module first,and judges the shading modes of PV modules according to the bifurcation point position of the S-V curve,and further judges the shading ratio by the overall integral area. The temperature and irradiance are normalized to make the method applicable for all working conditions. Combined with the PV module power optimizer,it is verified that the proposed diagnosis method has a high accuracy rate and can accurately estimate the shading area of each PV module.