Based on the low efficiency of sizing, slime of underflow, the separation and other problems, contrast test was conducted under original condition, reducing the material concentration, unlocking the closed cycle and reducing the material concentration of φ500 mm and φ710 mm classifying cyclone in Xingtai Coal Preparation Plant, the 3 groups of experimental data was analyzed. The result showed that after unlocking small closed cycle and reduce feed consistence, fine particle of feed was reduced obviously, the underflow with fine particle was changed, classification efficiency indicators were improved obviously, which improved the classifying effect of classifying cyclone.