Abstract: Laboratory-scale sieve analysis and experiments on rates of flotation of both sized and unsized coal are conducted to explore the law governing the variation of yield and ash of concentrate product in the flotation process. Test result shows that in terms of flotation rate, the highest is the 0.250～0.125 mm size, which is followed in order by the sizes of 0.500～0.250, 0.125～0.075, 0.075～0.045, and ＜0.045 mm. The flotation rate of the unsized coal depends on that of each size fraction, and with the increase of flotation time, its flotation rate tends to decrease along with rise of ash of concentrate. As for the concentrate yield and ash in relation to flotation time in flotation of each size fraction, a mathematical model is developed using the software Excel. And based on these models and the size analysis data, a similar mathematical model for flotation of whole size range of coal is finally derived. Comparison of the model-derived data with experimental data well demonstrates that the modeling is in good agreement with the regularity in flotation of unsized coal and high in reliability and can accurately predict the technical indices of flotation process.