In recent years, air pollution has been getting increasingly serious in ChinaA cause of great concern for the government and general public. Research on air pollution has focused mainly on the environmental and climatic effects, such as the increasing number of haze days, reduction in visibility, human health impacts, suppression of global warming, extension of cloud life, restriction of light precipitation, and weakening of the East Asian monsoon. In fact, the exacerbation of air pollution might also affect the radiation balance of the surface-atmosphere system, with subsequent direct impacts in areas of socioeconomic concern like agricultural production. However, domestically, research in this area is currently lacking. Accordingly, the present study, based mainly on the sunny diffuse radiation fraction (SDRFdefined as the diffuse solar radiation divided by the total solar radiation in conditions of sunny weather) at 47 stations over China, combined with CO_2 emissions data, aerosol optical depth (AOD) and sunshine duration data, analyzes the spatiotemporal variation of SDRF in China and the possible determining factors. The results provide a reference and basis for the accurate assessment of terrestrial ecosystem productivity and its carbon budget. Analysis of the SDRF distribution reveals clear regional characteristics in China, with relatively larger values distributed mainly in the Sichuan Basin and Central China. However, the values of SDRF in Yunnan, Xinjiang, Tibet and Northeast China are small. The majority of stations show an obvious upward trend in SDRF, especially in Eastern China, where the upward trend is more significant than in other regions. Therefore, after removal of the effects of cloud, aerosols should be considered a factor with important influence on the SDRF during the past 50 years. Analysis of the characteristics in each region shows that the increase in SDRF is more obvious in North China, East China and Central China than in South China, Northeast China, Northwest China and Southwest China. This indicates that, in regions where air pollution is more serious, the decline in SDRF is more significant. Sunshine duration in sunny weather is highly correlated with SDRF, with the correlation coefficient in East China, Central China and North China often exceeding -0.8 (statistically significant at the 99.9% confidence level). This result implies that an increase in the concentration of aerosol particles in the air has a significant impact on sunshine duration and SDRF over China.