The method for producing alumina by adopting reverse floatation bauxite concentrate is characterized by that: a. using reverse floatation concentrate, lime milk and alkali liquor to prepare green ore pulp; b. preheating ore pulp to 220 deg.C, making desilicification and titanium-removing reaction, then more heating to 260-280 deg.C, making insulation resolution for 30-90 min, in the insulation tank, c. crystal seed decomposition adopts one-stage method including high-temp. agglomeration, low-temp, growing up and intermediate cooling process to make crystal seed decomposition to produce alumina; and d. making settlement and separation of red mud.