Solar spectrum plays an important role on electrical performance of PV modules via affecting their short circuit current. In this study, a new model combining the impacts of both air mass and diffuse solar radiation ratio is developed to evaluate the solar spectrum impacts on the short circuit current of photovoltaic (PV) modules. A new method, named air mass cumulative distribution function method (AMCDF), is introduced to represent the relationship between air mass and solar spectrum effect. The experimental data shows that when air mass is less than 4.5, the relationship between the normalized short-circuit current and the air mass cumulative distribution function can be well represented by a five order polynomial. However, when air mass is larger than 4.5, the relationship becomes irregular. Further study on the irregular data indicates that the chaotic relationship is caused by the impact of diffuse solar radiation ratio (R-d). Based on these findings, the new model which combines the air mass cumulative distribution function and the diffuse solar radiation ratio is developed to evaluate the spectrum effect. Compared to conventional models, the proposed model has higher prediction accuracy and it also can predict short circuit current even when the air mass is high. (C) 2018 Elsevier Ltd. All rights reserved.