For the balanced proportional mixing device, the mixing process of the foam solution mixture is to add pressure into foam solution through foam solution pump, and then introduce the pressured foam solution into balance valve. After being adjusted in the balance valve, the foam solution is send to the proportional mixer. When the change of water pressure and flow rate in the main pipeline occurs in different working conditions, the balance valve is always able to dynamically adjust the volume of the foam solution that has been introduced to the mixer, so that foam solution with accurate proportion can be formulated without interruption during the operation of the device, which is then supplied to the foam extinguisher to generate quality foam for effective fire fighting work. This device is especially suitable to be used in medium to large foam fire extinguishing systems. Since the normal pressure foam solution storage tank allows continuous filling of foam solution during the process of fire fighting, which will prolong the time of fire fighting, the anti-disaster ability and reliability has greatly improved. Balanced proportional mixing device is a comparatively more advanced foam fire extinguisher, which especially fits significant fire protection projects in petrochemical enterprises, large scale oil depot and oil wharf, as well as offshore drilling platforms.