The invention relates to a heavy metal ion adsorbent and an application thereof. A preparation method of the heavy metal ion adsorbent comprises the following steps: taking main stem tobacco stalk as a raw material, and performing the steps of specific surface area increasing, immersion by a mixed solvent of low molecular alcohol and aqueous alkali, and solid-liquid separating in order to obtain the heavy metal ion adsorbent. The heavy metal ion adsorbent takes the main stem tobacco stalk as the raw material, and is obtained by the steps of specific surface area increasing as well as immersion by the mixed solvent of low molecular alcohol and aqueous alkali for modification; the tobacco stalk and the tobacco leaf are homologous, the composition of the tobacco stalk and that of the tobacco leaf are basically same, a non-tobacco component cannot be introduced into a tobacco extract, the tobacco stalk has a lot of the metal ion latent adsorption sites, so that the tobacco stalk can create conditions for heavy metal ions adsorption through modification, and the adsorption test proves that the adsorbent has good absorbing effect for heavy metal ions in the tobacco extract.