The invention discloses a method for preparing a lithium manganate battery cathode material. The method comprises the following steps of: melting a mixture of molten salt and a reactant through heating, and cooling, washing, filtering and drying to obtain the lithium manganate battery cathode material according to the stoichiometric ratio of a chemical formula LiCoxMn2-xFyO4-y, wherein x is more than or equal to 0 and less than or equal to 0.1, and v is more than or equal to 0 and less than or equal to 0.1; manganese metal powder is taken as a manganese source; lithium nitrate or lithium chloride is taken as a lithium source; and KCl is taken as a cosolvent. A lithium manganate product prepared by adopting the method has the advantages of good crystallization, stable electrochemical performance, high charging and discharging capacity, excellent cycle performance, less preparation process, simple process, low equipment requirement, cheap raw material price, and low cost and can be industrially produced.