In order to analyze the mechanical properties of trees in the natural disasters, the characteristics of trunk and branch structures were studied in the paper. And a rapid method of parametric models was represented using family table and UDF library of Pro/E. On the base of taking into account of the fractal characteristics of trees, which include selfsimilarity and selfaffine, the models of trunk and branches layered and stepped were constructed. Through setting and modifying parameters, such as length and angle of branch, the generating and reconstructing of geometrical models for tree structure were implemented rapidly. The results show that the method of parametric models is effective in establishing tree structure.