The invention relates to a method for preparing a lithium-enriched lithium manganese oxide solid solution cathode material. The method comprises the following steps of: adding a mixed aqueous solution of nickel salt, cobalt salt and manganese salt into an oxalic acid or oxalate aqueous solution by an oxalate coprecipitation high-temperature solid state method, and stirring and reacting to generate nickel, cobalt and manganese oxalate coprecipitation; performing solid and liquid separation, washing and drying to obtain a nickel, cobalt and manganese oxalate precursor; and mixing and grinding the precursor and lithium salt, drying, baking at high temperature in an air atmosphere, and thus obtaining the lithium-enriched lithium manganese oxide solid solution cathode material. During preparation of the precursor, the proportion of the nickel salt, the cobalt salt and the manganese salt is adjusted, so that the constituents of the lithium-enriched lithium manganese oxide solid solution cathode material can be adjusted flexibly. The preparation method is suitable for large-scale, economic, stable and reliable production of the lithium-enriched lithium manganese oxide solid solution cathode material, has obvious advantages, and is high in practical value.