Using the secondary settling tank effluent, this paper is going to research the potentials of three coagulations (polyaluminium chloride, ferric sulfate, and self-polymeric aluminum ferric) in deep chemical phosphorus removal by the beaker experiment. The experiment focuses on the dosages, the hydraulic conditions of coagulation and effect of pH on the removal. The results show that three coagulants have good efficiencies in phosphorus removal. After coagulant treatments, phosphorus can be decreased below 0.5mg/L and achieve Grade A standards of urban sewage treatment plants (GB18918-2002). The removal efficiencies of polymer silicate are superior to those of poly aluminum chloride and polymeric ferric sulfate.