In the existing literature, there are many studies focused on the scattering-weakening effect of different atmospheric constituents (gas, aerosols, liquid particles, etc.) on solar radiation, but few quantitative studies on the scattering-weakening effect of solar radiation by fog and haze. In this paper, the scattering-weakening effect of fog and haze on daily global solar radiation is investigated based on principal component analysis (PCA). First, the influence of different fog and haze levels on daily global solar radiation is analyzed. For example, in Tianjin, China, the average weakening degree is as follows: they are 18.66%, 26.37%, 37.32%, and 45.58% in light, moderate, heavy, and serious pollution respectively. Second, 7 types of global solar radiation weakening models (GSRW models) based on air quality index (AQI) are proposed. The measured data indicates solar radiation is gradually weakened with the increase of AQI, but the weakening speed gradually slows down. Besides, GSRW models are applied to six Chinese regions with fog and haze, and the results show that these models have good applicability (the average R value is 0.730, RMSE is 0.059 and MAPE is 9.430), especially for heavy air pollution regions.