Abstract: This research extracted essential oil from shallot under the condition of vacuum distillation extraction assisted by ultrasound.The investigation of single factors was studied,and then orthogonal optimization test was proceeded.The best conditions of shallot essential oil extraction were that the ratio of material to liquid was 1 ∶ 1,ultrasonic power was 75 W,ultrasonic time was 7 minutes,the temperature of vacuum distillation was 50 ℃,and vacuum distillation time was 90 minutes.Under these conditions,the yield of shallot essential oil was 1.21%,and the content of thiosulfinates was 69.12%. In addition,the GC- MS confirmed 23 kinds of substances of the shallot essential oil,including 54.33% sulfurous substances.