Abstract: In order to determine how the diameter class length distribution (DCLD) of fine roots of Chinese fir (Cunninghamia lanceolata) would be affected by soil warming, nitrogen addition and their interaction, a factorial experiment of soil warming (ambient, +5 ℃) and nitrogen addition (ambient, +4 and +8 g N·m^-2·a^-1) was carried out in the Chenda State-owned Forest Farm in Sanming, Fujian Province. An expanded extreme value model fitted the DCLD of roots of all the six treatments very well (R²=0.97). The model parameters showed that soil warming reduced the total root length, but its effect on root diameter was not significant. Nitrogen addition decreased both total root length and root diameter. The interaction of soil warming and nitrogen addition had significant effects on total root length, but had no significant effects on root diameter. DCLD of fine roots under the six treatments could be fitted well by the extreme value function (R²>0.98). The correlation analysis showed that specific root length for roots of 0-1 mm diameter was significantly negatively correlated with the parameter c, and the actual total root length was significantly positively correlated with the parameter b. It was concluded that the root morphology of Chinese fir seedlings would respond to both soil warming, nitrogen addition and their interaction, and these responses could be reflected by the changes in parameters of the extreme value model.