The invention relates to a method for preparing calcium fluoride and in particular relates to a method for preparing calcium fluoride from waste acids of hydrochloric acid and hydrofluoric acid. The method mainly comprises the following steps: dropwise adding waste acids and a calcium chloride solution, controlling the mole ratio of calcium fluoride to hydrogen fluoride to be 1:(2.1-2.15), and further reacting for 1-1.5 hours after dropwise adding is completed; keeping the temperature at 40-50 DEG C, stirring, and performing a reaction for 2 hours; standing still to settle down so as to obtain a calcium fluoride solid and filtrate, namely a hydrofluoric acid solution which is thickened to 12-18.6%; precipitating, washing, and filtering, thereby obtaining a calcium fluoride product. The method provided by the invention is large in calcium fluoride granularity, easy in filtration, simple in process and low in production cost, calcium fluoride and hydrofluoric acid can be recycled, and the problem of pollution of conventional industrial fluorine-containing waste acids can be thoroughly solved.