Abstract: The essential oil from Cyperus rotundus L. is extracted by supersonic with mixed solvent. The chemical components were identified and their relative contents were measured by GC/MS. The main components are α-copaene (1.97%), cyperene (15.73%), α-bisabolene (2.14%), α-gurjunene (1.29%), 2-methoxy-8-methyl-1,4-naphthalenedione (4.01%), β-selinene (17.99%), oxo-α-ylangene (3.00%), 4,4α,5,6,7,8,hexahydro-4α,5-dimethyl-3-(1methyl ethylidene)-2(3H)naphthalenone (8.11%), α-cyperone（26.15%）, longipinocarvone (1.11%), etc. These high content compounds are the characteristic components of Cyperus rotundus L., which we recommend as the index of identification and quality estimation of the medicine.