The composition of the flower essential oil from Citrus aurantium L. var. amara Engl was analyzed by gas chromatography-mass spectrometry (GC-MS), and its physicochemical characteristics was determined. The DPPH, ABTS, hydroxyl radical scavenging rate and total antioxidant capacity were determined to evaluate the antioxidant activity of this kind of essential oil. The results showed that this essential oil was an amber clarification liquid with the characteristic aroma of Citrus aurantium L. var. amara Engl flower. Forty-one kinds of components were isolated from the essential oil, accounting for 95.80% of the total, including 13 kinds of alcohols (59.34%) and 16 kinds of terpenes (22.82%), 4 kinds of alkane, three kinds of acids and ester, one kind of indole and one kind of phenol. The essential oil has a good antioxidant activity, and its total antioxidant capacity exceeded VC at high concentrations. Its scavenging ability of DPPH free radical was weak, and the scavenging rate of 50 mg/mL essential oil was 73.51%. However, Its scavenging abilities of ABTS and hydroxyl radical were better, and the scavenging ability of 10 mg/mL essential oil was 85.63% and 94.87%, respectively. It was found that the antioxidant capacity of this essential oil was positively correlated with its concentration.