The present invention discloses a vehicle-mounted large-flow fire-fighting foam fluid mixing system, including a supply kit, a mixing kit, a control kit, and a pipeline kit. The supply kit includes an auxiliary gas supply device, a fire pump, an integrated foam pump, a fire pump main motor, and a coupling. The mixing kit includes a fire monitor interface, a foam generating device, and a fluid mixing device. The control kit includes a foam mixing proportion single-chip microcomputer control system, an alarm module, a power module, an auxiliary air compressor switch module, a frequency converter, and a central control display screen. The pipeline kit includes an air drainage tube, a fire hose, a foam liquid pipe, and a pipeline valve. For the problems of flow fluctuation and low foam foaming efficiency, the present invention optimizes the design and adopts a new control policy, thereby implementing precise mixing under the large-flow condition.