Garlic is a perennial herbaceous plant of the Liliaceae family and is rich in nutrients. Garlic oil is the main functional ingredient in garlic and has anti-tumor, cardiovascular system protection, and blood sugar lowering effects. The reason why garlic oil has a wide range of pharmacological effects is that garlic oil contains a variety of organic sulfides, including diallyl disulfide (DADs) and diallyl trisulfide (DATs). as the main active ingredient. This experiment first studied the composition differences between steam distillation garlic oil and supercritical CO2 extraction garlic oil, and discussed the reasons for the differences. Then, commercially available garlic oil was used as raw material to study the distillation temperature, vacuum degree, feeding speed, scraper The influence of membrane rotation speed and separation stage on the effect of molecular distillation determines the process conditions for multi-stage molecular distillation to improve the quality of garlic oil. The main test results are as follows: 1. Differences in the main components of steam distilled garlic oil and supercritical CO2 extracted garlic oil. The highest content in steam distilled oil is DATs (including isomers), which is 36.21%, accounting for three thirds of the total volatile oil. More than one third, followed by DADs and diallyl tetrasulfide compounds, with contents of 24.75% and 15.03% respectively. The contents of DADs and 3-vinyl-1,2-dithia-5-cyclohexene in supercritical CO2 extracted garlic oil are relatively high, 29.88% and 21.65% respectively, followed by 3-vinyl-1,2- Dithia 4-cyclohexene is 11.60%, while the content of DATs and diallyl tetrasulfide is lower, among which 3-vinyl-1,2-dithia 5-cyclohexene and 3- The total content of vinyl-1,2-dithia-4-cyclohexene is 33.25%, accounting for one-third of the volatile oil. The total sulfide content in steam distilled garlic oil is higher than that in supercritical CO2 extracted garlic oil. 2. The method for detecting active ingredients in garlic oil by gas chromatography was determined. The results showed that the retention times of DADs and DATs were 11.212min and 16.228min respectively. Under the operation of this method, DADs and DATs achieve high precision (2.041%, 4.780%, respectively) and recovery rate (100.449% and 101.795%, respectively), which is suitable for the determination of the active ingredient content of garlic oil. 3. Determination of the optimal process conditions for first-level molecular distillation. The effects of distillation temperature, distillation vacuum, feed speed, and film scraping speed on the refining effect of active ingredients in garlic oil were studied. According to the single factor test results, the L_9(3~4) orthogonal test was used to determine the optimal process conditions for first-level molecular distillation. The results show that the distillation temperature is 50℃, the distillation vacuum is 200Pa, the feed speed is 1.5mL?min-1, and the scraping speed is 200rpm. 4. Determination of the optimal process conditions for the second-level molecular distillation. Using the distillate from the first-level molecular distillation as raw material, the effects of distillation temperature and vacuum degree on the purity and yield of the active ingredients in the distillate were studied. Orthogonal experiments were used to determine the optimal process conditions for secondary molecular distillation. The results show that the distillation temperature is 45°C and the distillation vacuum is 150Pa. 5. Determination of the process parameters of the third-stage molecular distillation. Using the distillate of the second-stage molecular distillation as the raw material, the changing trend of the distillation temperature on the distillation amount of DADs and DATs in the distillate was studied. The process conditions of three-stage molecular distillation were determined as follows: distillation temperature 40℃, vacuum degree 100Pa. 6. Determination of separation stages After five-stage molecular distillation, the purity of DADs and DATs in the obtained garlic oil reached 85.03%, and the yield was 54.35%.