Abstract: The investigation was carried out to study the effects of microbial inoculation amount, pretreatment time and pH on reverse flotation of microbial pretreated Wangping high ash coal and the mechanism of microbial reverse flotation. We compared the reverse flotation performance of microbial pretreatmentwith the conventional reverse flotation methods and found that the method of microbial pretreatment showed obvious effect on reverse flotation. When the volume of microbial inoculation was 8 mL with a pretreatment time of 4 d and pH 7, the yield of cleaned coal can be up to 76.78 % and the ash content is 38.66 % reduced by 13.73 % from the feed coal, which prove that the reverse flotation method of microbial pretreatment can effectively distinguish the cleaned coal and mineral.While for the conventional reverse flotation experiments, at the optimum reagent conditions with a dosages of dodecylamine1000 g/t and dextrin 600 g/t, the yield of cleaned coal can be up to 88 % but the de-ashing effect is not ideal with the ash content of 38.66%, which indicate that conventional flotation agents have poor selectivity between cleaned coal and mineral.