The thermal behavior and decomposition reaction kinetics of 2-nitroimino-5-nitro-hexahydro-1,3,5-triazine (NNHT) were investigated by TG-DTG and DSC under atmospheric pressure and flowing nitrogen gas conditions. The results show that the thermal decomposition process of NNHT has two mass loss stages. The exothermic decomposition reaction mechanism obeys chemical reaction rule. The kinetic parameters of the reaction are E(a)=131.77 kJ mol(-1), lg(A/s(-1))=12.56, respectively. The kinetic equation can be expressed as: dalpha/dt = 10(12.86)(1-alpha)(3/2)3(-1.5849 x 10(4)/T)). The critical temperature of thermal explosion of NNHT obtained from the peak temperature (T(p)) is T(bp)=467.22K. The entropy of activation (DeltaS( not equal)), enthalpy of activation (DeltaH( not equal)), and free energy of activation (DeltaG( not equal)) of the reaction are -7.978 J mol(-1)K(-1), 127.99 kJ mol(-1) and 131.62 kJ mol(-1), respectively.