Abstract: The Supercritical carbon dioxide fluid extraction (SFE) technique was applied to extract the oil of Xinjiang Nigella Sativa L seeds. First we have optimized the SFE extraction conditions by using single-factor and orthogonal testing methods. Second we have determined the fatty acid components in the oil that was extracted by SFE using GC-MS. the results showed that the optimized conditions for the SFE of oil from Xinjiang Nigella Sativa L seeds were as follows: extraction press20MPa, extraction temperature 35℃, extraction time 1.5 h ,CO2 fellow 25kg/h. Under these conditions, extraction yield could up to36.12%. the results of GC-MS analysis shows that the main contents of them are unsaturated fatty acids, in which the relative content of 9,12-Octadecadienoic acid was 60.95%, 9-Octadecenoic acid was 20.54%,eicosenoic acid was 2.43%， the total content of unsaturated fatty acids were 84%。SFE are can selective extraction unsaturated fatty acid which in the Nigella Sativa L seeds，It is worth popularizing and promising extraction and separation technology.