Abstract: This study examined the change of soil carbon affected by the increaseof biomass crops and more phenol and organic acid input in soil due to elevatedCO₂ concentration. A culture experiment using soil from a field after being cultured one year under FACE platform with two CO₂ levels (ambient CO₂ and elevatedCO₂) and two N levels (normal N and low N) was conducted in a greenhouse at thesame N treatment with the field. The results indicated that compared to soil from ambient CO₂, turnover of different soil particles in soil from elevated CO₂ was increased and affected by added straw and nitrogen levels. Soil carbon content in particles of size >250 and <53 μm was increased due to input of phenoland organic acid under straw added or not condition. Soil carbon content in each particle per unit of soil was increased and the increase magnitude was larger in particles >53 μm. The change was larger at normal N with no straw and at lowN with straw added. The results indicated that straw, phenol and organic acid played a more important role and had great significance in soil carbon sequestration under elevated CO₂ conditions. However, the effect of decomposition of strawon carbon in different particle sizes was dependent on different N levels, which was known poorly and should be investigated further.