Objective To explore the dominant ecological environment factors and stand control factors for the formation of large-diameter wood of Cunninghamia lanceolata in Nanling Mountains, investigate their influence rule and provide a theoretical guidance for cultivation and management of large-diameter wood stands of C. lanceolata in Guangdong Province.Method Based on the investigation of the existing large-diameter wood stands of C. lanceolata in Nanling Mountains, the site index (SI), soil integrated fertility index (I), micro-topography index (M) and geographical index (G) were extracted and the index evaluation system was established. The relationships of large-diameter wood volume (V_l), output (O_l), proportion (N_D≥26), outturn percentage (Y_l) with each index were analyzed.Result There were significant positive correlations of each index of large-diameter wood with SI, M (P<0.01), the correlation coefficients were 0.37-0.44 and 0.22-0.33 respectively. V_l、O_l and N_D≥26 had significant positive correlations with I (P<0.05), the correlation coefficients were 0.24-0.39. V_l and O_l showed a gentle quadratic curve trend of slowly increasing first and then slowly decreasing with the increase of reserved density (D), the correlations were significant (P<0.05). There were no significant correlations of G, stand age (A) with each index of large-diameter wood. The large-diameter wood output at the age of 20-30 was predicted by a quantitative model: O_l=${{\rm{e}}^{{\rm{5}}{\rm{.781 + 0}}{\rm{.004}}\;{\rm{SI + 5}}{\rm{.004}}{A^{{\rm{ - 1}}}}{\rm{ + 0}}{\rm{.261}}\ln D{\rm{ - 45}}{\rm{.151S}}{{\rm{I}}^{{\rm{ - 1}}}}}}$(R=0.62, P<0.01).Conclusion SI, I, M and D are the dominant impact factors for growth of large-diameter wood in Nanling Mountains. It is benefitial for large-diameter wood formation when SI is above 18, the soil has higher porosity, moisture and nutrient contents, the micro-topography condition is a shady and concave slope below 35° in the lower part, and the reserved density is 1 100-1 300 plants·hm^-2.