The invention belongs to the technical field of preparation of coal mine fire prevention and extinguishing materials, and in particular relates to a preparation method of a mine inhibitor. The method is as follows: preheating distilled water, polyethylene glycol and N,N-Ethylene Bis-stearamide for reaction under N2 protection, then adding vinyl acetate, Dichloromethylvinylsilane and a catalyst for thermal insulation reaction, then adding dropwise an initiator to continue the thermal insulation reaction, cooling and collecting reaction mixture, distilling the reaction mixture, collecting distilled residue to evenly mix with tert-butanol and copper powder, and collecting a mixture to obtain the mine inhibitor. The mine inhibitor has the characteristics of good inhibition effect AND long inhibition service life, the reaction process is less in heat release, and the mine inhibitor has no fire hazard, can effectively prevent the spontaneous combustion and dust raising in coal storage and transportation process, and has a good application prospect.