The impeller of CLF flotation cell adopts the high specific speed backward inclined blade impeller. The shape of the lower blade is consistent with streamline that the pulp through the gap between the impeller blade with weak agitation power, which can guarantee the pulp carry out the inner loop along the specified path. The upper pulp flows downward to false bottom through the circulating path, and enters to the impeller area under the action of differential pressure produced by inflation area and airless area and the suction force of impeller, then passes through the grid plate and forms the superposed layer above the grid plate. The coarse-grained minerals suspend in over the grid plate, the grid plate shortens the climbing dist of mineral laden bubble, makes the coarse-grained minerals in the state of shallow-tank flotation, reduces the turbulent flow of pulp in the upper area of tank, and builds a stable separation zone and froth bed.