It is difficult to keep the flight speed of the aircraft constant because the spraying system in the aircraft is operating in flight and the aircraft is liable to be disturbed by the external environment in flight. In the process of spraying pesticide, the aircraft should achieve the rated flight speed and must go through an acceleration phase, and in the process of spraying to the end of farmland or completing spraying, the aircraft must also go through a deceleration phase. Therefore, when the pump motor and/or the nozzle motor keep the rotational speed constant, if the above situation occurs, there will be a problem that pesticide is sprayed unevenly when the aircraft sprays pesticide.