Abstract: In order to find the thermal dynamical effect of the exothermic materials on the mechanical capability of the nuclear explosive device, the thermal physics analysis of the nuclear explosive device with public hypothetic models was done. The heat-producing power of weapon-grade plutonium (WgPu), weapon-grade uranium (WgU) and depleted uranium (DU) per kilogram were calculated through simulation and dynamic decay cascade, the regression line was fitted and analyzed. The temperature fields of the nuclear explosive device raised by Steve Fetter were analyzed according to the simulation results of the heat-producing power of the exothermic materials. The hypothetical models of the nuclear explosive device were modified according to the normal disposal method in industry manufacture, and thermal stress distribution was simulated with the information processed before. The results show that the thermal dynamic properties of the four types of hypothetic nuclear explosive models raised by Steve Fetter are very bad, so they can’t exist in reality.