In order to prevent the spontaneous combustion of coal efficaciously, a new kind of compound material of multiphase foamed gel is obtained, which is composed of fly ash, foaming agent, thickener, crosslinker, and nitrogen and formed by physical and mechanical stirring. It makes use of the all-around capability of gel, foam, grouting, and inhibitor to prevent mine fires. The formation and crosslinking mechanism of multiphase foamed gel were analyzed in theory, and the effects of the mass fraction of foaming agent and slurry, the quantitative ratio of polymers, and concentration and solid particle on foam properties were carried out. Meanwhile, the resistant property and inhibition characteristic of multiphase foamed gel were studied experimentally and theoretically. The multiphase foamed gel provides a new technical method to prevent the coal spontaneous combustion and thereby it has a vast potential and development prospect.