The unsymmetrical dimethylhydrazine(UDMH) and initial oxidation products were characterized by gas chromatography-mass spectrometry,and the content of main components were identified. The results show that the oxidation sample contains dimethylamine,UDMH,unsymmetrical dimethylhydrazone,formaldehyde dimethylhydrazone,N-nitroso dimethylamine,acetaldehyde dimethylhydrazone,1,1,4,4-tetramethy-1,2-tetrazene and dimethyldizene in initial oxidation stage under oxidation time minor to 100 h in air,and the content of dimethylamine,formaldehyde dimethylhydrazone and N-nitroso dimethylamine increas in this stage,but the content of dimethylamine decreases and that of N-nitroso dimethylamine increases quickly while forming new oxidation substances in the following process. The presentation of fragment ion peak of m/z=42～43 in all the MS spectra of the compounds containing nitrogen proves that the break reaction of N—N bond in molecules of UDMH and organic oxidation products containing nitrogen easily take place under heating.