The invention provides an inactivation processing method for undisturbed soil. The method comprises the steps including sampling of the undisturbed soil, wrapping processing of the undisturbed soil and high-pressure vapor inactivation processing. The method provided by the invention has the advantages that a wrapping manner which combines a TPU waterproof gas-permeable film and gauze is adopted, so that entering of external moisture into the soil is reduced; during inactivation processing of the undisturbed soil, the problem of increase of a soil water content caused by the entering of too much water vapor into the soil can be overcome to the hilt; the method implements improvement and innovation of existing methods; in a carbon flux observational research with direct absorption of atmospheric CO2 by the soil, changes in water contents of the undisturbed soil and the inactivated soil can be reduced to the hilt; and the method is highly important and meaningful for accurate determination of direct CO2 absorptivity of the soil and explanation of absorption courses of the soil.