Objective: The chemical components of the essential oil in the Fructus Foeniculi from 10 areas were analyzedby GC - MS. Method: The essential oil was extracted from Fructus Foeniculi by steam distillation, the componenls were analyzed with different kinds of capillary columns, the optimum separation and analytical conditions were studied, the amount of the components from the essential oil were determinated by normalization method. The components separated were identified by GC-MS. Chromatographic conditions were: Capillary column HP-5 (30m×0.25 mm, 0.25Um) ; column temperature 50℃ (10 min) 2℃ ·min →50℃(1 min) 5℃·min→200℃(5 min); split injection,split ratio 30: 1; injector temperature 250℃ . Mass spectrometer conditions were: ionization mode: El, electron energy 70 eV , interface temperature: 280C , ion source temperature: 200℃ , quadropole temperature 100℃ , mass scan range: 35-500 AMU, solvent delay 3.0 min. Results: Twenty components constituting above 94% of the total essential oil were separated and identified. The relative content of trans - anethole was 65%-78% , it might be used for quantifying purpose. Their total ion chromatograms (TIC) are similar, but there is a little difference in the TIC and the relative percentage contents. Their similar components may be used in identification of Fructus Foeniculi. Conclusion: The method is reliable, stable and reproducible, this method can be applied to the analysis of the essential oil components extracted from Chinese traditional medicine.