Abstract: Larix principis-rupprechtii natural forest was taken as research object.Based on 1531 strains of individual tree crown width measured data,the study was conducted on the natural forest of larch wood single crown width model.Firstly from the nine common crown width diameter candidate models,a model with higher accuracy of fitting was selected as the basic model of crown width model,then from the tree size and vigor factor,site factors and stand competition factor were screened with the crown width of a strong correlation factors as independent variables in the model for modelling,finally,the model is tested and evaluated by using the deviation,the residual root mean square error R and the determination coefficient and combined with the likelihood ratio test.As a result,the 3 parameter logistic forms crown width diameter model fitting with highest accuracy,and the model parameters can be explained.Therefore,the model can be used as the basis of the model of Larix principis-rupprechtii single crown width model;the object of trees crown length,stand density and competition index has strong correlation with crown width.When these factors are considered in the basic model.the model can further improve the prediction accuracy.The crown width model constructed in this research fills the blank of Larix principis-rupprechtii natural individual tree crown width model.

Key words: Larix principis-rupprechtii, natural secondary forests, crown width model