In order to explore the preference of Cunninghamia lanceolata for different nitrogen forms, unravel the response characteristics of the lateral roots development and photosynthetic physiology of C. lanceolata seedlings under different forms of nitrogen, and thus provide a theoretical basis for rational management of nitrogen fertilizer for C. lanceolata, we investigated the effects of NO₃^-N, NH₄⁺N, and NH₄NO₃ (3 mmol·L^-1 nitrogen) on the lateral roots growth, CO2 exchange parameters and chlorophyll fluorescence characteristic of C. lanceolata by using 3monthold C. lanceolata seedlings. The results showed that: (1) different forms of nitrogen significantly influence the biomass of shoots and lateral roots, and the most higher biomass both for shoots and lateral roots were observed in NH₄⁺N treatment, follows by NO₃^-N treatment, NH₄NO₃ treatment was the lowest. (2) Under NH₄⁺N and NO₃^-N treatments, the biomass of shoots and lateral roots in total roots length, total roots surface, and total roots volume were significantly higher than that of NH₄NO₃ treatment (P＜0.05), and the above root morphology parameters in NH₄⁺N treatment were significantly higher than that in NO₃^-N treatment as well (P＜0.05), while no significant differences were noted in lateral roots number among different nitrogen form treatments (P＞0.05). (3) The photosynthetic rate, stomatal conductance, and transpiration rate in leaves of C. lanceolata seedlings were obviously higher in NH₄⁺N treatment than that in NO₃^-N and NH₄NO₃ treatments, while no difference was observed between NO₃^-N and NH₄NO₃ treatments. (4) NH₄⁺N treatment significantly decreased the initial fluorescence, while increased the maximal fluorescence, variable fluorescence, and PSⅡpotential efficiency as compared with NO₃^-N treatment. The above results indicated that NH₄⁺N treatment not only increased the stability of PSⅡ reaction center, but also maintained a higher photochemical activity and electron transfer rate in PSⅡ reaction center，which ultimately improved the growth of C. lanceolata. Therefore，from the growth of lateral roots and photosynthetic characteristics in leaves of C. lanceolata under different nitrogen forms, it can be deduced that among different forms of nitrogen, C. lanceolata seedlings was much preferences for NH₄⁺N.