Cymbopogon Citratus from Hainan Province was extracted through distillation extraction to obtain essential oil. It was found that extraction time, solid-liquid ratio, grass particle size, plant part, and extracting solvent affect the yield and the components of the essential oil. The yield varied from 0.09% to 1.06%. When 50g dry Cymbopogon Citratus with the length of 2 cm was extracted with1400mL water containing 8 g sodium chloride for 180 min, the oil yield was 1.06%. Although a considerable chemical variability was observed, the essential oils were mainly composed of linalool, neral, geranial, geraniol, and geranic acid. The total amount of the five compounds varies during 86-96%. Hydroxyl radical scavenging antioxidant activity of the essential oil was examined through electron paramagnetic resonance. The scavenging ability of 1% oil solution in ethanol was about 32%.