Abstract: Mine fires seriously hinder the safe production of coal, but three-phase foam is an effective approach to prevent the mine fire. At present, the existing two-phase foam generatorsare not suitable for preparing three-phase foams. In order to develop a foam generator suitable for the preparation of three-phase foams, it is necessary to conduct in-depth analysis on the physical foaming characteristics of three-phase foam and optimize the structure of the foam generator. Accordingly, in view of the characteristics of the three-phase foam, this paper takes the self-priming foamer as an example to analyze the foaming characteristics and formation principle of the three-phase foam and its foamer.The distribution law of the 〖JP2〗flow field, pressure and turbulence intensity of the mixed slurry inside the foamer, and an optimization scheme of the self-priming foam generator are proposed. The results show that:① The self-priming foam generator uses the natural pressure difference to inject the flame-retardant gas into the pipeline to realize the full mixing of the gas and the slurry. The difficulty in the design of the self-priming foam generator is to maintain a sufficient natural pressure difference to break the bubbles and particles. ② When the mixed slurry flows through the Venturi tube, the velocity and turbulence intensity both increases first and then decrease along the flow direction, and reach the maximum value near the throat. The negative pressure area in the pipe is distributed in the throat, while the maximum negative pressure is close to the wall of the pipe. It is more favorable to generate three-phase foam by opening holes in the pipe wall near the throat to eject flame retardant gas. ③ Although an appropriate increase in the diffusion angle can increase the maximum velocity and turbulence intensity at the same time, the degree of improvement gradually weakens with the increase of the diffusion angle; in addition, the maximum negative pressure value increases first and then decreases with the increase of the diffusion angle; When the diffusion angle is 55°, and the opening position is near the throat of the pipe wall, it is most favorable for the generation of three-phase foam.