OBJECTIVE：To compare the chemical constituents of petroleum ether fraction from ethanol extract of Aconitum sinomontanum before and after processing. METHODS ：After A. sinomontanum was purified with water ，the raw product decoction pieces were prepared ；the raw decoction pieces were steamed with licorice juice under high pressure to prepare processed decoction pieces of A. sinomontanum . The petroleum ether fractions of raw product and processed product were obtained after ultrasonic extraction with 95％ ethanol. The chemical constituents in the samples were analyzed by GC-MS. NIST 2014 mass spectrometry database was used to compare and match the components . The peak area normalization method was used to determine the relative percentage content of each component. RESULTS ：Before and after processing ，fatty acids and esters were the main components in the petroleum ether fraction from ethanol extract. Totally 18 chromatographic peaks were detected in the detection pieces of raw product，and 13 compounds were identified ，accounting for 94.60％ of the total content of volatile components. The components with relatively high content were （Z，Z，Z）-9，12，15-octadecatrienoic acid （26.13％），hexadecanoic acid ethyl ester （25.27％）， palmitoleic acid （10.84％），ethyl linoleic acid （10.67％），（Z，Z）-9，12-octadecenoic acid methyl ester （6.66％），pentadecanoic acid（5.11％）and so on. Totally 25 chromatographic peaks were detected in the decoction pieces of processed products，and 18 components were identified ，accounting for 82.40％ of the total content of volatile components. The components with relatively high content were palmitoleic acid （18.95％），（Z，Z）-9，12-octadecenoic acid methyl ester （17.93％），hexadecanoic acid ethyl ester（11.94％），（Z，Z，Z）-9，12，15-octadecatrienoic acid （10.54％），（Z，Z）-9，12-octadecenoic acid （5.51％），（Z）-11-hexadecanoic acid（5.30％）and so on. After processing ，7 new components were added ，5 of which were identified as （－）-eucalyptus globulus alcohol，ethyl 2-methyltetrade-canoate，6-methyl-4-phenylcoumarin，β-sitosterol，heptadecane. After processing ，no components disappeared，and the content of some components increased or decreased. CONCLUSIONS ：After processing ，the volatile components in the petroleum ether fraction from ethanol extract of A. sinomontanum are different ，and（－）-eucalyptus globulus alcohol and other components are added after processing.