Abstract: A method for the monitoring of dihydroetorphine hydrochloride, a powerful anesthetic and analgesic drug , in biological fluid was developed by means of GC-MS with selected ion monitoring. Dihydroetorphine was extracted from human blood and urine with dichloromethane, and then was derivatized with N-heptafluorobutyrylimidazole after it was concentrated to drvness。A dihydroetorphine monoheptafluorobutyl derivative was formed ,which showed good characteristics on GC-MS with electronic impact mode.Its M⁺ was Besides, Besides this its main fragments includedm/z 576,534,522 and 508. These main ions were all selected as the ions of identification due to their relative Peak intensity and stability The detection limit was l pg. The target drug was identified based on its retention time multiple ion monitoring and relative peak intensity. This method has been successfully used for detection of dihydroetorphine hydrochloride in blood and urine from dilivdroetor-phine addict and poisoned patient , respectively. Good results have been obtained.