Solar radiation drives photosynthesis of vegetation. Changes in solar radiation received by ground surface affect the net ecosystem exchange of carbon dioxide (NEE) of forest ecosystem. In this study, we obtained 30min flux data and routine meteorological data at a planted subtropical coniferous forest in Qianyanzhou station. The clearness index was used to quantify the change in sky condition. Based on these data and index, the effects of changes in solar radiation received by ground surface on NEE were analyzed in midgrowing season (June to August) from 2003 to 2010. The results showed that NEE reached its maximum when the clearness index was 0.4-0.6 (a middle intensity of solar radiation). Compared with clear sky condition, the increase of diffuse radiation and the decrease of air temperature and vapor press deficit (VPD) under cloudy sky condition led to the increase of NEE. The NEE with clearness index of 0.4-0.5 and 0.5-0.6 was significantly higher than that with clearness index of 0.7-0.8. Clearness index with values of 0.6-0.7 and 0-0.1 occurred more frequently, suggesting that the sky condition and solar radiation received by ground surface under this condition were not optimal for the net carbon uptake of this forest ecosystem.