Differential Scanning Calorimeter（DSC），Accelerating Rate Calorimeter(ARC) and Reaction Calorimeter (RC) were used to study thermal hazard of dinitrotoluene(DNT) nitration. DSC results show onset temperature T0 of trinitrotoluene(TNT) is 298.38 ℃, which is lower than that of DNT. ARC results demonstrate that TNT starts to decompose at 232 ℃, and T_D24 of TNT decomposition is about 224 ℃. Based on RC test results, there is a large amount of heat release during DNT nitration, and the heat generation at 110 ℃ is 1.4 times heat generation at 90 ℃, in which a large part comes from the exothermal side reaction actually. Therefore, temperature should be controlled strictly to avoid acutely exothermal side reaction and product decomposition.