A rapid, simple and environmentally friendly supercritical fluid extraction and supercritical fluid chromatography coupled to mass spectrometry (SFE-SFC-MS/MS) method has been developed for the analysis of nine phenolic compounds in garlic. Through the optimization of the SFE parameters using response surface methodology (RSM), 15 phenolic compounds were successfully extracted at 50 °C in 9 min with the addition of 30% methanol using a method that was automatic, efficient, green and prevented oxidation. Moreover, the operating conditions of the SFC-MS/MS were also optimized for the analysis of the SFE extracts. 15 phenolic compounds in the garlic showed good separation performance on a Shim-pack UC-X Diol column, and 0.1 mM oxalic acid and 1 mM ammonium formate in methanol were chosen as the most suitable mobile phase components. Furthermore, a calibration curve was developed using a matrix-matched standard, and 9 phenolic compounds showed good linearity (R2 > 0.99). The limits of detection of the 9 phenolic compounds varied from 0.6 to 12 ng/g, and the quantifications ranged from 2 to 40 ng/g. The validation data also showed acceptable recoveries for 9 phenolic compounds, and the relative standard deviations (RSDs) for the overall precision were lower than 10%. The developed method has been utilized to analyze the phenolic compounds in garlic from different geographical areas of China (Cangshan, Jinxiang, Pizhou, Dali), which suggests that this off-line SFE-SFC-MS/MS method could be adapted to the quantitative analysis of phenolic compounds in garlic.