Based on the long-term field manipulation experiment, the response of understory plants to 7 years of nitrogen deposition in a Chinese fir(Cunninghamia lanceolata) forest was investigated. The quantities of experimental N added and treatment codes were N₀[(Control); 0 kg/(hm²·a)]; N₁[60 kg/(hm²·a)]; N₂[120 kg/(hm²·a)]; N₃[240 kg/(hm²·a)]. The result showed that the totally 51 species belong to 34 families, 45 generas. Along with the increase of nitrogen deposition, plant species, families and genera were all decreased. In addition, both Shannon-Weiner index and Simpson diversity index reduced, but Whittaker index increased with nitrogen deposition increase. Furthermore, Sorenson similarity index was decreased obviously. Detrended correspondence analysis(DCA) indicated that nitrogen deposition changed plant community composition. Plant species Smilax china and Ardisia punctata were found in the plots of four treatments, which would be the popular species. Plant species Ilex asprella, Ficus hirta, Camellia fraternal, Camellia trichoclada and Rhizoma cyperi were found in N₀-N₂ plots, which would be the resistant species. While Rubus parvifolius, Codonopsis lanceolata, Morinda umbellate, Ficus lyrata, Oreocnide frutescens, Callicarpa formosana, Herba cayratica and Lygodium japonicum were found in N₀ and N₁ plots, which would be less resistant species. Other 16 species such as Adinandra millettii and Cinnamomum parthenoxylon were only found in N₀ plots, which would be the sensitive species. In conclusion, because plant diversity in the subtropical forest was negatively affected by nitrogen deposition, more attention should be paid to the plant conservation.