Abstract: In order to investigate the difference between the low-rank coal particle-air / oily bubbles interaction,the rela- tionship between the total probability (E) and the flotation rate constant (k) of mineral particles entering the foam product by Sutherland theory was introduced. The flotation rate tests of low-rank coal particle-air / oily bub-bles were car- ried out. Furthermore,the induction times between low-rank coal particle-air / oily bubbles were cal-culated. The results of flotation experiments showed that the maximum flotation yield of low-rank coal particles in oily bubbles (95. 69% ) was much higher than that of low-rank coal particles in the air bubble (25. 99% ) with the same collector consumption. Meanwhile,the test results obtained by the 2015EZ induction timer indicated that the induction time (35 ms) between low-rank coal particles and oily bubble was significantly smaller than that (93 ms) between low-rank coal particles and air bubble. This demonstrated that the hydrophobicity of the oily bubble surface was much stronger than that of the air bubble surface. However,combined with the low-rank coal parti-cle-air / oily bubble flotation rate test,the induction time between the air / oily bubbles and low-rank coal particles obtained by Sutherland’s theory in the relationship be- tween the total probability of solid particles entering the foam product and the flotation rate constant was 9． 67 and 8． 46 ms,respectively,with little difference between the two. This was mainly due to that the air / oily bubble rising ve- locity in the real flotation process was 23. 26 and 22. 68 cm / s,respectively,which was much higher than the air / oily bubble collision velocity (2. 0 cm / s) during the 2015EZ induction timer test. In addition,during the back-calculated process of induction time,it could be found that the rising velocity of air / oily bubble had a significant effect on the back-calculated induction time. Therefore,the intrinsic reason that the oily flotation process was better than the tradi- tional air flotation process was revealed. It also demonstrated that the induction time between the low-rank coal parti- cles and the oily bubbles was smaller than that between the low-rank coal particles and the air bubbles.