To improve the water resistance of magnesium oxychloride cement (MOC) and transform the solid waste-titanium extraction tailings (TETS) powder into resources, the TETS powder was added into MOC as an admixture. The effect of TETS powder on the setting time, compressive strength, dissolution rate of chloride ion, phase composition, microstructure and pore structure was analyzed by Vicat, electronic servo testing machine, ion chromatograph, X-ray diffractometer, scanning electron microscope and mercury intrusion porosimetry, etc. The results show that untreated TETS increases the total porosity and the large pores (>100 nm in diameter) content of the MOC matrix, resulting in a decrease in the compressive strength and water resistance of MOC. TETS powder treated by grinding can improve the dispersion of MgO particles in the MOC system, promote the growth and development of 5Mg(OH)2·MgCl2·8H2O crystals, and reduce the total porosity of MOC, resulting in an increase in the compressive strength and water resistance of MOC. The 28 d compressive strength and 28 d strength retention coefficient of MOC containing 20% TETS powder treated by grinding (by weight of light-burned magnesia) reach to 102.4 MPa and 0.88, respectively. Meanwhile, the concentration of chloride ion in soaking liquid decreases to 11.2 mmol/L.