Orthogonal experiment was employed to optimize the extraction of linolenic acid from perilla seed by supercritical carbon dioxide extraction and the effects were investigated, such as extraction pressure, temperature, time and CO₂ flow rate on main fatty acid composition contents. The results showed that the contents of palmitic acid and stearic acid were negatively correlated with extraction pressure and time, had a change trend of descend firstly then ascend coinciding with temperature and CO₂ flow rate. Because the contents of oleic acid and linoleic acid had a change trend of descend firstly then ascend coinciding with CO₂ flow rate. There was a positive correlation between the contents of linolenic acid and extraction pressure and time because the change trend of temperature and flow rate was increased at first and decreased later. The optimal extraction conditions for linolenic acid were found to be 40 ℃ for 120 min with CO₂ flow rate 20 L/h under pressure 25 MPa, and the extraction rate of linolenic acid was 88.09% obtained under these optimal conditions. The perilla seed oil with the supercritical CO₂ extraction can meet requirements of standard plants edible oil.