GC retention index of volatilc component of Cyperus rotundus was studied by capillary Gas Chromatography, and the standard Gas Chromatographic diagram and GC retention in dex spectrum, which provide a new identification method for traditional Chinese medicine was established. This method may be used to difierentiate the genuine C. rotundus from other false or confusion products. The average CV (% ) of RI from 37 sets of C. rotundus from three differcnt producing areas were 0~0.24 The method posscsses well accuracy, comparability and good reproducibility