The invention discloses a modified absorbent and a preparation method thereof. The modified absorbent is characterized by containing the following components: activated carbon, polyethylene glycol, butyl rubber, sodium chloride, sodium bromide, polyvinyl alcohol, stearic acid, calcium carbonate, zinc oxide, paraffin oil, methylcellulose, rosin soap, phthalic acid dimethyl anhydride, phenolic resin, flatting agent and insoluble sulfur. The preparation method comprises the following steps: carrying out pretreatment and modification on activated carbon; carrying out halogenating modification on the butyl rubber; and mixing the residual components, adding the modified activated carbon and the modified butyl rubber, stirring, carrying out ultrasonic treatment, and finally extruding. The modified absorbent is used for processing common absorption substances, so that the static adsorption capacity is improved, and the water vapor transmittance is decreased; and the preparation process is simple and feasible and applicable to industrialization.