The invention discloses an eggplant straw modified activated carbon water purifying agent which is prepared from the following raw materials in parts by weight: 40-50 parts of eggplant straw, 110-120 parts of activated carbon, 3-6 parts of magnesium nitride powder, 10-15 parts of bentonite, 15-20 parts of industrial aluminum sulfate, 4-7 parts of jade powder, 4-7 parts of medical stone powder, 8-10 parts of sepiolite powder, 10-15 parts of corn starch, 4-5 parts of modified diatomite and a suitable amount of water. By using eggplant straw as a raw material for production, the eggplant straw modified activated carbon water purifying agent disclosed by the invention has the advantages of developed activated carbon pore structure, large specific surface area, high adsorption speed, good adsorption capability to various solutes, free gases and the like; the use of stone powder of bentonite and the like has the effects of bacterium inhibition, decoloration, ionic exchange and release of microelements beneficial to a human body; the use of aluminum sulfate can be used for flocculating pollutants in water. The eggplant straw modified activated carbon water purifying agent disclosed by the invention is safe, nontoxic, and suitable for water purification and indoor air purification.