Abstract: To study the change of soil carbon affected by increase of crops biomass and more carbon input in soil due to elevated CO₂ concentration, a culture experiment on soil from field under Free Air Carbon Dioxide Enrichment (FACE) platform with two CO₂ levels (Ambient CO₂ and Elevated CO₂) and two N levels (NormalN and Low N) was conducted in greenhouse at the same N treatments with field. Results indicated that compared to soil from ambient CO₂ concentration, turnover of different soil particle in soil from Elevated CO₂ concentration was increasedsignificantly and resulted in an increase of soil carbon amount in >53 μm and decrease in <53 μm. The change was larger at Normal N with no straw and at Low Nwith straw added. Carbon amount in bulk soil was increased and it increased morein treatment with increasing of active carbon into soil from root with straw; it was reverse with no straw treatment. However, the effects of decomposition of straw on carbon in different particle-size were dependent on it at different N levels and this was known poor and need more work to carry out.