The invention relates to a fire extinguishing agent spray system, a fire extinguishing agent spray method and an elevating fire truck. The fire extinguishing agent spray system comprises a first storage device, a second storage device, a first ejector, a conveying pipeline, a pressure control valve and a controller, wherein the first storage device is used for storing a fire extinguishing agent; the second storage device for storing blown gas and is connected with the first storage device so as to blow out the fire extinguishing agent when the blown gas passes through the first storage device;the first ejector is used for ejecting the fire extinguishing agent and the blown gas; the conveying pipeline is connected between the first storage device and the first ejector and is used for conveying a mixture of the fire extinguishing agent and the blown gas; the pressure control valve is arranged between the first storage device and the second storage device and is used for controlling an outlet pressure of the second storage device; the controller is used for calculating a pressure difference of the mixture of the fire extinguishing agent and the blown gas at an inlet and an outlet ofthe conveying pipeline, and is used for adjusting the control pressure of the pressure control valve according to the calculated pressure difference. The system and the method can automatically adjustthe pressure when the mixture of the fire extinguishing agent and the blown gas reaches an inlet of the first ejector.