Abstract: In order to understand correlation between different floatability evaluating indexes (K) in single size coal slime, flotation rate coefficient of subordinate function (flotation rate coefficient), calculation floatability and recovery of middling fractions combustible (Ec,md) were applied to evaluate floatability of single size coal slime. The results show that flotation rate of single size coal slime decrease in the following order: 0.125~0.074, 0.074~0.045, 0.25~0.125, 0.5~0.25 and -0.045 mm, calculation floatability decline in the following order: 0.125~0.074, 0.074~0.045, 0.25~0.125, -0.045 and 0.5~0.25 mm, and recovery of middling fractions combustible lessen in the following order: 0.25~0.125, 0.125~0.074, 0.074~0.045, 0.5~0.25 and -0.045 mm. The analysis of correlation of different evaluation indices indicate that flotation rate coefficient had strong correlation with calculation floatability, both of them can be used as basic indices to evaluate floatability of single size coal slime. By contrast, recovery of middling fractions combustible has little correlations with floatability of single size coal slime，which only can be used as a reference index to evaluate floatability.