The invention relates to a device for purifying indoor air through ternary ion polymerization technique. The device provides a ternary polymer ion, which is formed by mixing oxygen ion, negative ion and titanium ion, to purify indoor polluted air. The ternary ion combines with the water in the air to catalyze and form photoactive groups with strong oxidizability. The photoactive groups comprise hydroxyl free radical (.OH), superoxide anion free radical (O2.), active oxygen (HO2., H2O2) and the like. The groups can oxidize and decompose various organic compounds and some inorganic substances by decomposing organic pollutants into non-polluting water (H2O) and carbon dioxide (CO2). The device can effectively remove the chemical pollutants in the air, including formaldehyde, benzene, TVOC and the like, and achieve the purpose of improving indoor environment and purifying air.