The influence factors, adsorption isotherm and kinetics of phosphate removal by modified steel slag were investigated in this study. In addition, the modified steel slag was applied to the phosphate removal of effluent after biological treatment. Result showed that the concentration of total phosphorus decreased to 0.678 mg/L and the removal rate reached 93% after adsorption by modified steel slag at 10 mg/L of initial phosphorus concentration, 10 g/L dosage of modified steel slag and pH 7;The adsorption of phosphorus by modified steel slag was in accordance with the Langmuir isotherm model and the theoretical saturated capacity was 1.98 mg/g. The adsorption process could be well described by the pseudo second-order kinetics(R₂>0.99). Furthermore, in the treatment of domestic wastewater, the total phosphorus concentrations of effluent reached the first B grade discharge standard of GB18918-2002 after treated by modified steel slag for 2 hours with a dosage of 50 g/L.