The fragmentation pathways and mechanisms of dialkyl（≥C2） dimethylpyrophosphonate were studied under electron impact（EI） condition using gas chromatography mass spectrometry（GC-MS） and gas chromatography tandem mass spectrometry（GC-MS/MS）.The parents of ions were found by MS/MS in parents scan mode,and the products of ions were found in product scan mode.The relationship of ions in EI mass spectra were built,while the fragmentation pathways were gotten.The main fragment ions were interpreted using the basic mechanism of ion fragmentation of radical site and charge site initiation theory.The experimental result showed that the EI mass spectra of most of dialkyl（≥C2） dimethylpyrophosphonate released no molecular ions.The fragment ions of m/z 175,158,157,143,97,79,65 and 47 were found in all EI MS of dialkyl（≥C2） dimethylpyrophosphonate.For the dialkyl dimethylpyrophosphonate,the reaction of molecular ions initiated at the radical site and charge site of unsaturated oxygen,saturated oxygen and π bond.The molecular ions produced different fragment ions from the α-cleavage reaction and inductive-cleavage reaction with hydrogen rearrangement.These fragment ions continued to fragment and produce ions from α-cleavage,i cleavage and other reactions.The fragmentation rules of dialkyl dimethylpyrophosphonate could provide a reference for the analysis and identification of this kind of compounds and other similar chemicals.