Abstract: Characteristic glycoside constituents were extracted from peony roots of 13taxa and 6 commercial drugs,and their constituent HPLC-plots were obtained by HPLCwith a 3.9×250mm column of YWG-CN,the solvent system of MeCN-(MeCOOH-MeCOONa-H₂O,pH 3.2)-CHCl₃(10:90:1,v/v/v),and the internal standard of asprin.The similarity of peony glycoside HPLC-plots among the samples was calculated by a computer according to the principle and methods of the quantification theory Ⅲ.The positions among the samples were expressed by the space coordinate.The similarity comparison was made among them and between different species and their varieties in their space distances obtained by the quantification theory Ⅲ.The method was used to not only identify unknown-commercial drugs or unknown plants but also compare the similarity among plants clearly.