Abstract: The paper described the improved grinding efficiency of the oolitic hematite from western Hubei Province in the presence of sodium hexametaphosphate（SHMP）,and mechanism of SHMP used as grinding aids was analyzed by measuring the viscosity and pH value of the grinding pulp，the surface potential and morphology of particles after grinding. The results presented that the contents of -0.074 mm in the grinding products was increased by 30.25% by keeping other grinding parameters as constant and with the addition of 0.8% (mass ratio of the sample) of SHMP. By lessening the viscosity of pulp，raising pH value，changing the surface potential of the particles，reducing the amounts of fine ore grains sticking to granules and acting on the micro cracks on the ore grain surface，SHMP could work by all of these patterns to promote the crushing environment and then increase the grinding efficiency.

Key words: Oolitic hematite from western Hubei province, Sodium hexametaphosphate, Grinding aids, Grinding efficiency, Mechanism