Chestnut shell active carbon is prepared by the following raw materials by weight: 120-140 parts of chestnut shell, 3-5 parts of zinc chloride, 4-6 parts of Arabic gum, 4-6 parts of periston, 25-30 parts of bentonite, 10-15 parts of alumina, 20-25 parts of pumice, 2-4 parts of lanthanum chloride, 2-4 parts of cerium chloride, 2-4 parts of scandium chloride, 2-4 parts of yttrium chloride, 2-4 parts of praseodymium chloride, 1-3 parts of lanthanum nitrate, 1-3 parts of cerium nitrate, 1-2 parts of scandium nitrate, 1-2 parts of yttrium nitrate, 1-2 parts of praseodymium nitrate, 4-5 parts of modified diatomite, and a proper amount of water. Chestnut shell is used as a raw material, so as that the active carbon has advantages of developed aperture structure, big specific surface area, high adsorption speed, and good adsorption capability on various solutes and dissociation gases; lanthanum chloride is used for activation so as to form active carbon, which has big gaps and strong adsorption capability, is suitable for absorbing organic matters in air and water and removing harmful substances like formaldehyde, is low in cost, and is suitable for industrialization production.