The invention discloses a formaldehyde purifying agent which is prepared from, by weight, 10-18 parts of magnetite, 6-8 parts of diatomite, 7-15 parts of activated carbon, 14-16 parts of bentonite, 20-35 parts of amomum, 19-24 parts of ash bark, 5-10 parts of lavender, 2-8 parts of cloves, 4-10 parts of chrysanthemums, 3-7 parts of mint, 7-9 parts of folium artemisiae argyi, 5-12 parts of cinnamon, 2-8 parts of horseradish tree leaves, 3-31 parts of spathiphyllum, 6-9 parts of adiantum, 4-8 parts of ivy tree bark and 4-10 parts of aloe. The air purifying agent does not contain harmful chemical matter or additives, can effectively remove formaldehyde in indoor air and can kill bacteria in the air and purify the air.