Abstract: Forestry surveying and estimation are one of the most important business for forestry management.Tree volume measurement used table is one of the most important method in the forestry property evaluation.A better algorithm is the key for estimative precision of model.This paper,based on parametric identification of Marquardt nonlinear model,takes an example of Commonly Used Two-Way Tree Volume Model,elucidates the least-squares minimization of nonlinear parametric estimation and analyzes error of estimative algorithm.Quadric algorithm based on quadric function approximate is applied to improve estimative precision of Tree Volume Model.Forestry resources’s surveying sample data is tested for improved algorithm.The result shows that the improved algorithm can improve more 10 percent estimative precision than that of old algorithm.