The Cook-off test of RDX explosive was carried out. The test results of explosives were discussed by the theoretics of thermal transfer. The thermal response of the explosive was calculated by numerical simulation methods and PHOENICS software was used in the simulation. The results show that RDX explosive decomposes slowly in the lower temperature (e.g. 205 ℃,230 ℃) and the heat of the reaction can be absorbed in time by the environment. Thus the thermal explosion is not occurred. And the calculation result has a good agreement with the experiment. When the test temperature is lower (e.g. 240 ℃),the temperature of the center of the column increases quickly. It will be ignited firstly. But in the higher temperature (e.g. 330 ℃), the higher temperature area is formed at the edge of the column. The temperatures of the area increase rapidly and lead to the thermal ignition and explosion.