The invention discloses a method for concentrating sulfur with sodium fluorosilicate mother liquor as activator of pyrite. The method includes the technological steps that first, the pyrite is obtained after flotation of lead and zinc is performed on lead, zinc and sulfur polymetallic sulfide ore, the pyrite contains a great amount of free CaO and 16-30% of FeS2, the pyrite is ground till the fineness of -200 meshes larger than 80%, and the solid content of ore pulp is 20-45%; second, the sodium fluorosilicate mother liquor is added into the ore pulp, activating reaction is carried out, the reaction time is 30-60min, and the pH of the ore pulp is 4.5-6.0 after the reaction is finished; third, the ore pulp after the reaction is fed into a flotation machine, meanwhile, flotation reagents are added, sulfur concentrate is obtained after air inflation and bubble scrapping are finished, and the adding method of the flotation reagents includes the steps that the flotation reagents accounting for 60-80% of the total amount are added before the flotation of the ore pulp, and the rest of the flotation reagents are evenly added stage by stage after every stage of flotation before discharge of tailings. With the method, the quality of the concentrated sulfur concentrate and the sulfur recovery rate can be guaranteed, activator cost is saved, and pressure on environmental protection is relieved.