With the aid of the Free-Air Carbon Dioxide Enrichment (FACE) system and the isotope ¹³C technique, effects of elevated atmospheric p CO₂ and nitrogen fertilization on replacement rate of soil organic carbon (SOC) in wheat field, through planting wheat (Triticum aestivum L. cv Yangmai 14) under a rice/wheat rotation system in a C₄ soil, on which only maize had been planted for years. Results show that after one crop of wheat, the value of δ ¹³C in SOC fell significantly, suggesting that wheat growth had altered the composition of SOC, and that elevated atmospheric p CO₂ stimulated the crop to transfer more organic carbon into the soil, thus increasing the SOC replacement rate in the wheat field from 3.61% to 6.72% when the nitrogen application rate was 150 kg hm^-2, LN and from 4.59% to 8.55%, when the application rate was 250 kg hm^-2, HN, or by 72.7% and 86.1%, respectively. It is quite obvious that elevated atmospheric p CO₂ and higher nitrogen application rate will accelerate SOC replacement in farmland soil.