The supercritical CO2 extraction technology was used to extract volatile oil from Ocimum basilicum L. The technical conditions affecting the extraction (pressure,temperature and time) were optimized by using orthogonal design, and the constituents of the volatile oil were studied by analyzingGC/MS. The results showed that the optimal conditions were , using 12 MPa of pressure , at 45 ℃ temperature and extracted for 2 h. Under this conditions, the extraction ratio was 0.761%. GC/MS analysis identified 30 compounds in the volatile oil. The main chemical component was terpenoids, which accounted for 96.64% of the total volatile oil. The relative content of the highest was linalool, containing 69.83% , followed by the (+)-Epi-bicyclosesquiphellandrene (6.73%) and 1,8 -Cineole (5.01%).