The invention discloses a tobacco leaf modulation method for preset power failure emergency treatment of an air source heat pump tobacco curing barn. The method comprises temperature and humidity regulation and control during normal power supply and ventilation and dehumidification device control during power failure. Temperature and humidity regulation and control during normal power supply are carried out by adopting a method of'heating, dehumidifying and promoting smooth hot air among tobacco leaves' in the tobacco leaf modulation process of the air source heat pump tobacco curing barn whenthe power supply is normal; the ventilation and moisture removal device is controlled by a method of slightly opening an air inlet door and fully opening a moisture removal window during power failure, and the temperature of the tobacco loading chamber is gradually reduced, so that water is not accumulated on the surfaces of tobacco leaves. Through temperature and humidity adjustment when power supply is normal and a method of slightly opening an air inlet door and fully opening a moisture exhaust window during power failure, the temperature of an air source heat pump tobacco curing barn anda tobacco loading chamber is gradually reduced during power failure in the tobacco leaf modulation process, water is not accumulated on the surfaces of tobacco leaves within a short period of time, and the tobacco leaves are little or free of loss. The method has no obvious difference from the quality characteristics and appearance characteristics of the tobacco leaves after normal power supply modulation, and the technology has high stability.