The work aims to put forward a fireproof thermal insulation structure to be fixed on the grain end against the blast of explosive-containing assembly in an accidental fire in order to lower the explosive part’s temperature rise and avoid explosive blast. The mathematical model involving explosive thermal decomposition reaction was established by finite element thermal analysis. The crucial process in the course of heat transfer and general laws of thermal responses of the assembly in fire accident were analyzed. In view of the economical, portable and operable design principle, a lot of very pertinent thermal control measures were adopted to design a three-layer fireproof thermal insulation on the grain end. The inlayer steel shell surface was polished so as to reduce surface thermal radiation. Meanwhile bolted connection among butt flanges was canceled to avoid thermal short circuit. In conclusion, the numerical analysis and experimental results show that the structure can effectively delay the explosive part’s temperature rise, prevent explosive reaction in accidental fire and help improve the safety of the containing explosive assembly.