Abstract: In this paper, the L-E method which has been applied to singular chain systems is extended into tree structure systems and its coefficient matrices are analyzed in detail. This paper compares these matrices of tree systems with those of chain systems and obtains a lot of valuable results. The methods of "dividing Lane" and "voidroad" presented in this paper have several advantages, such as high efficiency, less difficulty and less work in the modelling, and easiness of programming. The work done in this paper enriches the theories of robot dynamic modelling.