The invention discloses a method for preparing sludge with strongly-acidic fluorine-containing waste water to prepare calcium fluoride concentrate. The method includes the steps that 1, calcium fluoride sludge is pre-treated and pulped after being treated, the calcium fluoride sludge, a trapping agent, a foaming agent and an adjusting agent are mixed and stirred, and the mixture is subjected to flotation, wherein the trapping agent is one or more of oleic acid, sodium alkyl sulfate, sodium naphthenate and modified fatty acid salt compound sodium dodecyl benzene sulfonate, the foaming agent isone of terpenic oil, methyl isobutyl carbinol and butyl ether oil, and the agenting agent is prepared from an activator, an inhibitor, a dispersant sodium carbonate and a flocculant; 2, the calcium fluoride sludge obtained after flotation is mixed with an acid solution; 3, the calcium fluoride sludge obtained after being treated in the second step is mixed with a fluorine-containing solution; 4, acalcium fluoride sludge mixture obtained after being treated in the third step is neutralized through an alkaline solution, the calcium fluoride sludge mixture is after-treated, and the calcium fluoride concentrate is obtained. The method has the advantages of being high in refining degree and achieving resource utilization of multiple industries.