Abstract: The size effect of hematite particles in flotation was studied by the pure mineral flotation experiments.The adsorption capacity of collector YSB on different grain size hematite was measured.At the same time,the flotation collision probability of particle and bubble and floating probability of different sizes hematite were calculated in theory.The results showed that the four different particle size of hematite were in speed for 1900r/min,slurry concentration is 20%,pH=6~7,collecting agent YSB dosage of 25mg /L under the condition of flotation recovery rate reaches the maximum value,but-15 μm size fractions of recovery rate is lower than that of the other three coarse.Also when the particle size is reduced to 15 μ m,the collision probability of mineral particles and the bubble is only 0.35%,floating probability is1.38%,resulting in recovery rate is greatly reduced.