[Objective] This study aimed to develop a method for extracting volatile oil from green-orange peel by reduced-pressure steam distillation. [Methods] A volatile oil tester was combined with a vacuum device for the extraction of volatile oil from green-orange peel, and a regulating valve in the device controlled the vacuum level. The composition and content of volatile oil under reduced pressure and atmospheric pressure were determined by gas chromatography-mass spectrometry (GC-MS), and the in vitro antioxidant activity was evaluated. [Results] The optimum process for the extraction of volatile oil by reduced-pressure steam distillation was: particle size of 8 mesh, solid-liquid ratio of 1∶7 (g/mL), vacuum of 0.082 MPa, time of 40 min, yield of 1.769 mL/100 g. 163 kinds of components were identified in the volatile oil of green orange peel extracted by reduced-pressure steam distillation, which was 33 kinds more than that by atmospheric pressure steam distillation, and the content of major components was increased. The scavenging ability of the volatile oil extracted under vacuum to superoxide anion free radical and hydroxyl free radical was significantly higher than that extracted by atmospheric steam distillation. [Conclusion] The reduced-pressure steam distillation volatile oil extraction has the characteristics of low temperature, short time, high yield, simple operation, and high operability. The obtained volatile oil has a good antioxidant effect, and the method is suitable for the extraction and separation of heat-sensitive substances.