Atmospheric nitrogen deposition is thought to have profound effects on terrestrial ecosystems. There have been many studies on the effects of nitrogen deposition on the aboveground parts of plants in the past few decades. However, the effects of nitrogen deposition on the belowground parts of plants are unclear. A simulated nitrogen deposition experiment was conducted to investigate the impact of nitrogen deposition on fine root stoichiometry of Chinese fir (Cunninghamia lanceolata) seedlings in Chenda State-owned Forestry Farm, Sanming, Fujian Province. Including ambient nitrogen deposition, three nitrogen addition levels were set:control (CK, ambient + 0 kg N hm^-2 a^-1), low nitrogen (LN, ambient + 40 kg N hm^-2 a^-1), and high nitrogen (HN, ambient + 80 kg N hm^-2 a^-1), with 5 replicates per treatment. The ingrowth donut method was applied to measure the stoichiometry of fine roots, including concentrations of C, N, and P, and the C:N and N:P ratios. The results showed that:(1) Nitrogen addition decreased the fine root C concentration in 2015; after that, LN treatment had no effect, but HN treatment increased the fine root C concentration. HN treatment increased the fine root (especially 0—1 mm root) N concentration, but LN treatment had no significant effect or significantly decreased fine root N concentration in July 2016. Nitrogen addition had no significant effect on fine root P concentration in 2015, but resulted in a decrease of fine root (especially 0—1 mm root) P concentration in 2016. (2) HN treatment significantly reduced the C:N ratio of fine roots in January 2015 and January 2016, while LN treatment significantly increased the C:N ratio of fine roots in July 2016. LN treatment had no significant effect on fine root N:P ratio, whereas HN treatment significantly increased fine root N:P ratio at most sampling times.(3) The C concentration and the C:N ratio of fine roots showed an increasing trend, but the concentration of fine root N and the N:P ratio showed a decreasing trend with time. This study showed that the effects of nitrogen addition on the stoichiometry of fine roots varied with different nitrogen addition levels and were regulated by the dilution effect of seedling growth.