In this paper,treatment technology of phosphorus wastewater with sulphuric acid modified fly ash/slag mixture was studied by using methods of chemical precipitation and adsorption. Through single factor contrast experiments, influences of fly ash/slag mixture dosage, pH value, reaction temperature, stirring time, standing time on phosphorus removal efficiency were investigated in detail,and the optimum condition was determined. The experimental results showed that the phosphorus removal rate of treatment 10 mg/L simulate phosphorus wastewater was over 93% under the optimal conditions:fly ash/slag mixture dosage was 2 g/L, 25℃ reaction temperature,pH value was 8,10 minutes stirring time,2 hours standing time,which reached the first grade of the national standard for wastewater discharge.