The compound 3,6-bis-nitroguanyl-1,2,4,5-tetrazin (DNGTz) was synthesized and its thermal behavior was studied by differential scanning calorimetry (DSC) and thermogravity (TG-DTG). The data in DSC curve were used to analyze the thermal decomposition mechanism and kinetics using the methods of Kissinger, Ozawa and integral. Therefore, the thermal kinetic parameters of the activation energy and pre-exponential factor were obtained as 187.23kJ·mol^-1 and 10^15.01s^-1, respectively. The thermal decomposition mechanism is phase boundary reaction and the differential function is f(α)=1. Then, the thermal safety of DNGTz, the density (ρ=1.762 g·cm^-3) and thermal conductivity (λ= 0.1856 W·m^-1·K^-1) were estimated and the specific heat capacity (c_p) was measured to obtain the equation of c_p with T in a micro-calorimetry (Micro-DSCIII) which is c_p(J·g^-1·K^-1)=-2.8805+2.1283×10^-2T-2.3132×10^-5T²-1.1689×10^-8T³ (287K < T < 352K). Then, the thermal decomposition kinetic parameters, mechanism function and the equation of c_p, ρ and λ were combined to evaluate the adiabatic-time-to-explosion (t_TIad= 8.16 s), the self-accelerating decomposition temperature (T_SADT=249.12 ℃), the thermal ignition temperature (T_be =262.31 ℃) and the critical temperature of thermal explosion (T_bp=277.68 ℃), thermal sensitivity probability density function S(T) vs T for DNGTz (infinite cylindrical, spheroidic or infinite platelike) with the radius of 1m surrounded with 300K, the peak temperature (T_S(T)max), safety degree (SD), critical thermal explosion ambient temperature (T_acr) and thermal explosion probability (P_TE). The thermal safety of the spheroidic sample is found to be better than that of the infinite cylindrical or infinite platelike sample.