Abstract: The subsurface lead-in fluoroprotein foam extinguishing system is worldwide applied. According to the proportional mixer, this system can be distinguished into two systems; the negative-pressure proportional mixer foam extinguishing system and the pressure proportional mixer foam extinguishing system. This article elaborates the applications of the negative-pressure proportional mixer and the pressure one in corresponding systems. In designing the negative-pressure proportional mixer foam extinguishing system, the pressure lead-in way can be applied. This can overcome many defects existing in the negative-pressure lead-in way. It is fit for the terminal (tank farm). The pressure proportional mixer foam extinguishing system has less dirigibility and adaptability. It can be only used in the place where the flow rate of the foam mixing solution is relatively constant.