Abstract: GC-MS was applied to the identification of chemical structure of easily gasifiable and thermo-stable organic impurities (i.e., 3.5-dibromopyridine, 2,4,6-trinitrobenzene, 2,4,6-trinitrotoluene and 4,6-dinitrobenzoisoxazole) in the purity SRM of hexanitrostilbene (abbr. as HNS); and LC-MS with APCI was applied to the structural identification of hardly gasifiable and poorly thermo-stable impurities, especially the non-polar intermediate of 1,2-bis(2,4,6-trinitrophenyl) ethane, (abbr. as DPE). Characteristic adduct ions of HNS and DPE were also detected by LC-MS with APCI. Organic impurities in HNS were successfully determined by the above mentioned methods which gave a sound base to eliminate the impurities from HNS and was beneficial for preparation of the purity SRM.