Ultrasound -assisted aqueous extraction method was adopted to extract oil from peony seed, and the fatty acid composition of the oil was analyzed by GC-MS. The effect of four parameters, including ultrasonic time, power, temperature and liquid/solid ratio on the extraction rate of peony seed oil were researched. On the basis of single factor tests，the extraction technology of peony seed oil was optimized by response surface methodology. The result showed that the optimum conditions obtained were as follows: extraction time was 54 min, extraction temperature was 45 ℃, liquid/solid ratio was 8.5∶1（mL/g）, extraction power was 960 W. Under this condition, the extraction rate of oil was 28.850 6 %. The predominant fatty acids in peony seed oil were linolenic acid methyl ester(40.04%), linoleic acid methyl ester (40.37%). The percentage of unsaturated fatty acids relative to total fatty acids was over 85%.