In China, the potential carbon sink of plantation could not be neglected because forest carbon storage increased significantly by afforestation in recent decades. In this study, CO2 flux was measured continuously using the eddy covariance technique over a 30-year aged mixed plantation in the hilly zone of the North China from 2006 to 2007. The major tree species are Quercus variabilis, Robinia pseudoacacia and Platycladus orientalis. The relationships between net ecosystem carbon exchange（NEE）and main meteorological factors were investigated. The results showed that daily mean nighttime NEE increased exponentially with an increase of air temperature (P<0.01). The temperature sensitivity (Q10) of ecosystem respiration was 1.92 in 2006 and 1.86 in 2007. On daily scale, NEE varied within a small range of ±5 g?m-2?d-1 when air temperature was lower than 10℃. Daily net carbon uptake by plantation increased obviously with air temperature when air temperature was more than 10℃. In the main growing season (April-September), daytime net carbon uptake was positively related with photosynthetically active radiation (PAR). The relationship between NEE and PAR could be expressed by the rectangular hyperbolic function. However, there was a linear relationship between NEE and PAR when vapor pressure deficit (VPD) was less than 1.0 kPa. In the main growing season, the apparent initial light use efficiency (α) averaged 0.032 in 2006 and 0.019 in 2007. The maximal assimilation rate (Pmax) averaged 0.96 mg?m-2?s-1 in 2006 and 1.10 mg?m-2?s-1 in 2007. Seasonal variation of Pmax and α was obvious. On monthly scale, Pmax had negative correlations with VPD (P<0.01) and PAR (P<0.05) but was not related with air temperature. No significant correlation could be found between α and PAR, VPD and air temperature.