Abstract:In this paper presented is a new method to describe stem form of trees. A stem could be divided into sections in equal length and volume could be worked out for each section, then "relative stem ratio" (RSR) was defined as the ratio between volume of each section and the total volume of whole stem.This new concept, relative stem ratio, implicates not only volume, but also diameter. RSR could be used as an index of tapering degree, because it was reduced progressively in the direction of stem length. The most important founction of RSR is to denote various forms of tree stems as series of diagram in quite uniform, therefore the changes of stem form and volume structure can obviously seen from the diagram. 8 major species of hardwoods in Changbai Mountain were analysed using this new methodology, the results were coincident wich those obtained from multivariate analysis.