The invention discloses a mixing device for a spraying machine. The device comprises a water tank, a check valve, a blade flow meter, a medicine tank, a float flow meter, a control valve, a mixing chamber, a liquid pump, a solenoid valve, a nozzle liquid end, a nozzle body and a nozzle gas end. The mixing device is characterized in that the check valve is connected to the water tank, the blade flow meter is connected to the check valve, the float flow meter is connected to the medicine tank, the control valve is connected to the float flow meter, one end of the mixing chamber is connected to the control valve, the other end of the mixing chamber is connected to the blade flow meter, the liquid pump is connected to the mixing chamber, the solenoid valve is connected to the liquid pump, thenozzle liquid end is connected to the solenoid valve, and a nozzle comprises the nozzle liquid end, the nozzle body and the nozzle gas end. The device remixes separated medicine and water, can ensurethat medicine liquid waste is avoided to the largest degree, can prepare medicine accurately, enables mixed medicine liquid to be more evenly and has the far-reaching research value.