Abstract: A method for the identification of adulterated soybean oil in peanut oil was established by chemometrics analysis software and GC-MS with headspace. MS information of peanut oil samples and soybean oil samples was collected by GC-MS with headspace, and the data were analyzed by chemometrics analysis software. The characteristic compounds of soybean oil were found out. Through methodological verification, characteristic marker of soybean oil was identified as 2,3-octanedione, with m/z 99.1 as quantitative ion. Linearity range of soybean oil was found in the range of 2.00%-100.0% (volume fraction), with detection limit (3s/k) of 1.14% and lower limit of determination (10s/k) of 3.80%. On the base of peanut oil sample, test for recovery was made by standard addition method; values of recovery found were in the range of 86.1%-105%, with RSDs (n=6) of determined values in the range of 1.3%-2.4%.