The invention discloses a method for preparing modified lithium nickel manganese oxide which is the anode material of a lithium ion battery. The method comprises the following steps: mixing a manganese salt material and a nickel salt material, and preparing a nickel manganese precursor through a sol-gel method; mixing the nickel manganese precursor and the nickel salt by using a three-dimensional oblique type mixing machine; presintering and high temperature sintering, and doping F- or F- and metal cations, then adding a metallic oxide and performing wet coating; and finally, acquiring a lithium nickel manganese oxide finished product by low temperature sintering, fluid energy milling and grading. The method provided by the invention uses an ion doping modification technology to improve the cycle performance and high temperature stability of the lithium nickel manganese oxide, and uses a wet coating technology to improve the high pressure cycle performance and high temperature stability of the lithium nickel manganese oxide.