A method for preparing lithium nickle cobalt manganese oxide, comprising the following steps: disassembling a waste battery and separating it, to obtain a positive electrode tab, a negative electrode tab and a diaphragm; mixing and grinding the positive electrode tab and a slagging agent, then drying, cooling, adding an aluminum powder, mixing well, to obtain a material; wherein the slagging agent includes one or more of calcium oxide, silicon dioxide or calcium fluoride, the weight ratio of the positive electrode tab and the slagging agent is: 1; and the weight ratio of a mixed material of the positive electrode tab with the slagging agent to the aluminum powder is: 1; conducting a self-propagating reaction to the material, cooling, and taking a lower layer of rough nickel cobalt manganese alloy; wherein the step of self-propagating reaction is putting the material into a self-propagating reactor, under an inert atmosphere, igniting a magnesium powder to initiate a self-propagating reaction; grinding the rough nickel cobalt manganese alloy, adding an alkali liquor, and then immersing, filtering, taking a filter residue for washing and drying, to obtain a porous nickel cobalt manganese alloy powder; adding a lithium salt solution to the porous nickel cobalt manganese alloy powder, mixing and dripping an alkali liquor, aging, filtering, taking a filter residue for washing and drying, to obtain a mixed powder of precursor; wherein the molar ratio of hydroxyl in the alkali liquor to lithium ion in the lithium salt solution is (1-1.3):1, the molar ratio of lithium ion in the lithium salt solution to a combined amount of nickel, cobalt and manganese in the porous nickel cobalt manganese alloy powder is (1.1-1.3):1; and sintering the mixed powder of precursor and cooling to obtain the lithium nickle cobalt manganese oxide. disassembling a waste battery and separating it, to obtain a positive electrode tab, a negative electrode tab and a diaphragm; mixing and grinding the positive electrode tab and a slagging agent, then drying, cooling, adding an aluminum powder, mixing well, to obtain a material; wherein the slagging agent includes one or more of calcium oxide, silicon dioxide or calcium fluoride, the weight ratio of the positive electrode tab and the slagging agent is: 1; and the weight ratio of a mixed material of the positive electrode tab with the slagging agent to the aluminum powder is: 1; conducting a self-propagating reaction to the material, cooling, and taking a lower layer of rough nickel cobalt manganese alloy; wherein the step of self-propagating reaction is putting the material into a self-propagating reactor, under an inert atmosphere, igniting a magnesium powder to initiate a self-propagating reaction; grinding the rough nickel cobalt manganese alloy, adding an alkali liquor, and then immersing, filtering, taking a filter residue for washing and drying, to obtain a porous nickel cobalt manganese alloy powder; adding a lithium salt solution to the porous nickel cobalt manganese alloy powder, mixing and dripping an alkali liquor, aging, filtering, taking a filter residue for washing and drying, to obtain a mixed powder of precursor; wherein the molar ratio of hydroxyl in the alkali liquor to lithium ion in the lithium salt solution is (1-1.3):1, the molar ratio of lithium ion in the lithium salt solution to a combined amount of nickel, cobalt and manganese in the porous nickel cobalt manganese alloy powder is (1.1-1.3):1; and sintering the mixed powder of precursor and cooling to obtain the lithium nickle cobalt manganese oxide.