Introduction2,6-Dinitro-4,8-bis(2,2,2-trinitroethyl)-2,4,6,8-tetraazabicyclo[3.3.1] nonane-3,7-dionel is a typical cyclourea nitramine. Its crystal density is 1.94 g/cm3. The detonation velocity corresponding to ρ=1.920 g/cm3 is about 8957 m/s. It has the potential application as high explosive due to the above-mentioned high performance. Its preparation[1], properties[1] and hydrolytic behavior[2] have been reported. In the present paper, we report its kinetic parameters and mechanism of the exothermic first-stage decomposition reaction studied with DSC, TG-DTG and IR.