The invention discloses a pneumatic ejection type liquid fertilizer applying device, system and method. The device comprises a pneumatic ejection type fertilizer applicator, a furrower and an adjusting rod, the pneumatic ejection type fertilizer applicator is arranged on the furrower, the furrower is fixedly connected with the adjusting rod, the adjusting rod is slidably and fixedly arranged on aframe, the system comprises an air compressor, an air storage tank, an air source treatment element, a pressure reducing valve, a liquid fertilizer box, a fertilizer quantity adjusting mechanism and the pneumatic ejection type liquid fertilizer deep applying device, the air compressor, the air storage tank, the air source treatment element, the pressure reducing valve and the pneumatic ejection type fertilizer applicator are sequentially connected, and the liquid fertilizer box, the fertilizer quantity adjusting mechanism and the pneumatic ejection type fertilizer applicator are sequentially connected. According to the device, liquid fertilizers can be atomized and deeply applied, the utilization rate of the liquid fertilizer can be increased, and agricultural non-point source pollution isreduced.