Analysis of oregano essential oil by gas chromatography quadrupole-time of flight-mass spectrometry (GC-QTOF-MS) with three capillary columns of different polarities to improve the qualitative accuracy by providing more retention indices to identify compounds.In addition,eight compounds with different contents in oregano essential oil were selected for a difference study between four quantitative analyses to optimize the quantitative accuracy.Twenty-four compounds were identified in the HP-5ms column,33 compounds were identified in the HP-1 column,30 compounds were identified in the HP-INNOWax column,and 15 compounds were present simultaneously in the three polar conditions,for a total of 38 compounds,accounting for more than 97% of the total essential oil content.Four methods (GC-QTOF-MS peak area normalization,GC-FID peak area normalization,internal standard method and external standard method) were used to determine the content of thymol,which were (25.869 ± 0.263)%,(27.567 ± 0.003)%,(7.396 ± 0.068)% and (5.558 ± 0.025)%,respectively.