It is necessary to adjust reaction pH when a single kind of PO43is used as phosphorus source to remove NH4+- N in a chemical precipitation process. However, this tedious step could be avoided in experiments that use the buffering effect of the composite phosphate and employ PO43and HPO42as phosphorus sources, pH was controlled by properly changing the proportion of PO43to HPO42-. The influences of pH, material proportion and different addition modes of magnesium on NH4+-N removal efficiency were investigated, with NH4+-N concentration in influent being 200 mg/L. It showed that the ratio of HPO42: PO43was concerned with phosphorus and NH4+-N removal. Under the condition that the total amount of phosphate is definite, the removal efficiency of NH4+-N decreased with the enhancement of HPO42concentration, while the efficiency of phosphorus increased. When increasing PO43concentration, it benefited the removal of NH4+-N, but the remaining phosphorus was high. The results showed that NH4+-N concentration decreased from the initial 200 mg/L to 39.14 mg/L with the remaining PO43at 5.14 mg/L if the ratio of HPO42: PO43remained at 1 : 3.