Abstract: The invention provides a method for preparing lithium manganese iron phosphate, which includes the following steps: S1: mixing a manganese source and/or an iron source in solid phase to obtain a first mixture; S2: sintering the first mixture in solid phase at 300° C. to 1200° C. to obtain a manganese iron oxide (MnxFe1?x?y)mOn; S3: mixing the manganese iron oxide (MnxFe1?x?y)mOn with a lithium source, a phosphorus source, and optionally a manganese source and/or an iron source in solid phase to obtain a second mixture; and S4: sintering the second mixture in solid phase at 350° C. to 900° C. to obtain lithium manganese iron phosphate LiMnxFe1?x?yPO4, wherein 0?x?1, and 0?y?1. The method of the present invention can be used to prepare a lithium manganese iron phosphate material with high tap density, long cycle life, low costs, and high cost-effectiveness.