A drug dosing device and method for dosage metering and control, the drug dosing device including a drug dosing canister, a first flow channel, a second flow channel, a third flow channel, a metering flow channel, a switch valve, a control valve and a pressure release port; the upper part or top of the drug dosing canister communicates with the upper part or top of the metering flow channel via the first flow channel; the lower part or bottom of the drug dosing canister communicates with the lower part or bottom of the metering flow channel via the second flow channel; the switch valve disposed on the second flow channel; the bottom or lower part of the metering flow channel communicates with the control valve via the third flow channel; the pressure release port is disposed at the upper part or top of the drug dosing canister; and the cross section area of the metering flow channel is less than the cross section area of the drug dosing canister.