The thermal decomposition of 1,4-dinitroimidazole was measured by DSC. Based on experiments,this paper studied the thermal rearrangement process for preparing 2,4-dinitroimidazole from 1,4-dinitroimidazole. The influences of reaction temperature and reaction time on the yield of 2,4-dinitroimidazole were discussed. An optional production condition was obtained by the experiments: reaction temperature 125 ℃,reaction time 3.5～4 h,yield 95%.