To understand soil CO2 emission variation trend and driving factors of different artificial woodlands under semi\|arid and erosion environment in the hilly area of the Loess Plateau, soil CO2 emission beneath three typical plantations of Prunus armeniaca, Hippophae reamnoides, and Robinia pseudoacacia were measured on August 2007，October 2007 and May 2008. Meanwhile some environmental factors which related with soil CO2 emission were also measured. The results showed that: (1) soil CO2 emission for different artificial woodlands was different and the daily value was 0.83-2.61μmol?m-2?s-1, 083-3.32μmol?m-2?s-1, and 0.80-3.45μmol?m-2?s-1 for Prunus armeniaca, Hippophae reamnoides, and Robinia pseudoacacia respectively, the soil CO2 emission of Hippophae reamnoides and Robinia pseudoacacia were higher than that of Prunus armeniaca; (2) different artificial woodlands had similar soil CO2 emission diurnal and seasonal variation trend, soil CO2 emission was higher in spring and summer; (3) significant correlation between soil CO2 emission and environmental factors was found after regression and correlation analysis, soil temperature was main factor from the whole year but in the spring and summer which were droughty the soil moisture was the main factor, besides, soil physiochemical characters and soil microbial biomass also could influence soil CO2 emission.