To enhance the efficiency and economy of mine fire control, the technology of three phase foam for preventing spontaneous combustion of coal in goaf is developed here. The producing flow of three-phase foam and main technical parameters are introduced briefly. Chemical dynamics equation was set up. According to controlling parameters in the equation: the reactant concentration of C and O2, the temperature (T) of coal and surroundings, the hole rate (?) of goaf, etc, the mechanism of three-phase foam for preventing spontaneous combustion of coal in goaf was studied. By the application of three-phase foam in workface N2703 of Daxing coal mine, which had been high temperature and fire point, the change on concentration of CO and O2 were contrasted in sampling gas and temperature in goaf. It had effectively prevented the fire. The result showed that the effect of three-phase foam for preventing spontaneous combustion of coal in goaf was excellent, and it is a new technology for mine fire prevention and with good prospect.