Cunninghamia lanceolata plantation which growed in Huitong of Hunan province was taken as research object,the relations between the sectional segments n of fallen trees,the volume v and the mean experimental form factors f_ε were analyzed.Regression method was used to establish an optimal regression model about sectional segments n and the mean experimental form factors f_ε.The optimal regression model is 公式.Through the scatter diagram of the sectional segments n and the mean experimental form factors f_ε,the optimal feasible sectional segments n_cis six.The results showed that the model′s precision was high and usability was powerful,which provides theoretical basis for finding the optimal feasible sectional segments .