The utility model discloses a foam preparation device. The technical scheme includes that the foam preparation device comprises a grouting pipe, a filter, a blow-off pipe, a pipeline mixer, a foam maker, an air inlet pipe, and an air feeder, wherein the filter is connected with an outlet of the grouting pipe, the blow-off pipe and the pipeline mixer are respectively communicated with the filter, the foam maker is communicated with an outlet of the pipeline mixer, the air inlet pipe is communicated with the foam maker, a check valve, a pressure gauge B and an air inlet pipe valve are sequentially installed on the air inlet pipe, the air feeder is connected with the pipeline mixer, the pipeline mixer comprises a mixer barrel body and a spiral piece, the spiral piece comprises left spiral pieces and right spiral pieces, the left spiral pieces and the right spiral pieces are fixedly arranged inside the mixer barrel body in a spaced mode, and the ratio of length to section diameter (L/D) of the pipeline mixer is ranged between 0-30. The foam preparation device is suitable for rapid extinguishing and effective prevention and control of coal spontaneous combustion fires in a coal mine.