Soil available carbon source and concentration regulate soil nitrogen transformation and soil nitrogen is affected significantly by carbon level in coniferous forest soil. Soil soluble carbon is higher in broad-leaved forest than that in coniferous forest, but the effect of carbon level on broad-leaved forest soil nitrogen is unclear. The broad-leaved forest (Castanopsis fargesii) soil from Wanmulin Nature Reserve in Fujian was selected and different carbon addition rates (0, 300, 600, 900, 1 000, 1 100 and 1 300 mg/kg soil added as glucose) were designed to study the effect of carbon on nitrogen after being incubated for 21 days at 25 ℃ and 60% of soil water holding capacity. The results showed that with the increase of carbon addition, nitrate nitrogen decreased rapidly and reached the minimum at 900 mg/kg soil. At this time, nitrate nitrogen decreased by 28.35 mg/kg. Soluble organic nitrogen (SON) decreased at 7th day with the amount of carbon addition, but at 21th day in the 900 – 1 300 mg/kg soil, SON was higher than that at 7th day, and SON from microbial after soil treated with the chloroform fumigation began to increase with carbon addition, increased by 15.09 – 17.10 mg/kg. Therefore, nitrate nitrogen was assimilated by the microbe into organic nitrogen, which reduced nitrate leaching or gaseous loss by denitrification risk in subtropical area in the case of more rainfall, whereas increased the risk of SON leaching. However, when nitrogen demand of ecosystem changed, SON could respond rapidly, so that the forest soil in this area could be effectively mineralized to meet the needs of plant growth, and improve the availability of nitrogen in the ecosystem. The nitrogen concentration in the litter of soil increased with more carbon addition, and nitrogen in the residual soil increased by 5.64 mg/kg. The IR spectrum showed that the carbon addition of 900 mg/kg decreased absorption peaks in the proportion of each wave number in residue after soil extracted by K₂SO₄ solution, and the effect of carbon addition was minimum in the highest absorption peak, 426 – 600 cm^-1 and 900 – 1 200 cm^-1. These results indicated that carbon addition increased nitrogen in mineral matrix and organic nitrogen in soil becomes more stable.