Abstract: With Japonica cultivar Wuxiangjing 14 as test material, a free-air CO₂ enrichment (FACE) experiment was conducted at Anzhen and Wuxi of Jiangsu Province in 2001～2003. The target CO₂ concentration of FACE plots was 570 μmol·mol^-1, 200 μmol·mol^-1 higher than that of ambient air. Three levels of N were supplied as LN (150 kg·hm^-2), MN (250 kg·hm^-2) and HN (350 kg·hm^-2). The effects of FACE treatment on the dynamics of rice tiller was studied, and the simulation model was established as T_t=A₁(1+e^a1-b1t₎-A₂(1+e^a2-b2t)+C×[B₁(1+e^a3-b3t)-B₂(1+e^a4-b4t)]+D. Where T_t was the numbers of rice tiller in t days after transplanting; A₁ and A₂ were the maximal tillers of production and death under ambient air, respectively; B₁ and B₂ were the maximal potential tillers of production and death under FACE, respectively; C was the coefficient of CO₂ concentration; D was the initial tillers after transplanting; and a₁, a₂, a₃, a₄, b₁, b₂, b₃ and b₄ were the control coefficients of the model. The dynamics of tiller numbers with the days after transplanting was described, and the model fitted well under ambient air and FACE conditions. Through testing with different year experimental data, the maximum and minimum RMSE was forecasted as 44.27 and 13.96 ind·m^-2, respectively, suggesting that the model was accurate and applicable.