The fire-fighting foam tank is mainly composed of a foam liquid pressure storage tank with a capsule and a PHYM type pressure proportional mixer made by using the Venturi principle. When the water in the system pipe network flows through the proportional mixer decompression orifice, the A pressure difference will be formed before and after. A part of the water (3% or 6%) at the high pressure enters the tank through the water inlet pipe of the foam tank, squeezes the capsule, and squeezes the foam liquid in the capsule through the liquid outlet pipe of the foam tank to the low pressure of the proportional mixer and the water. Mixing to form a foam mixture, the formed foam mixture is output to the foam generating equipment (medium, low and high multiple foam generators, foam guns, foam guns, etc.) to mix with air to produce foam fire extinguishing. The device is widely used in oil depots, chemical plants, hangars, oil fields, oil-fired boilers, underground garages and other places.