The invention relates to rich-lithium manganese-selenium-based anode material and a preparation method thereof and aims to solve the technical problem that existing rich-lithium manganese-based anode material is poor in rate capability and circulation performance. The formula of the rich-lithium manganese-selenium-based anode material is xLi2Mn1-ySeyO3.(1-x)LiMO2. The preparation method includes: preparing manganese salt and the soluble salt of M element into a mixed solution, simultaneously adding the mixed solution, the aqueous solution of a soluble selenium-containing compound, a precipitator solution and a buffer solution into a reaction kettle for reaction so as to obtain a composite metal precursor, well mixing a lithium-source compound and the composite metal precursor, and then calcining under the oxygen atmosphere to obtain the rich-lithium manganese-selenium-based anode material. The first charge-discharge coulombic efficiency of the rich-lithium manganese-selenium-based anode material is above 75%, the capacity retention ratio of the rich-lithium manganese-selenium-based anode material reaches above 95% after circulation of 200 circles under the 0.1C rate, and the rich-lithium manganese-selenium-based anode material is applicable to lithium-ion batteries.