Degradation analysis methods of PV modules using many outdoor Current-Voltage (I-V) curve data are proposed in this paper. The I-V curve data measured under various outdoor conditions are translated to the Standard Test Conditions (STC) by two kinds of translation procedures. Procedure.1 directly translates to the STC by linear interpolation method (LIM) with many reference I-V curves, which are created by I-V curve fittings. Procedure.2 is a combination of procedure1 and translation formula. Characteristic values such as maximum power, short circuit current, open circuit voltage, fill factor, series resistance and shunt resistance are quantitatively evaluated with both methods. Degradation rates of mono crystalline Si and polycrystalline Si modules were analyzed and accuracies were verified by comparing with indoor measurement results. Although open circuit voltage between the two proposed methods were different, the almost same annual degradation rates were obtained.