The invention relates to lithium ion battery, more particularly to a lithium nickel cobalt manganese oxide (Li(Ni0.8Co0.1Mn0.1)O2) composite material, including lithium nickel cobalt manganese oxide and a hydrophobic material coated on the surface of lithium nickel cobalt manganese oxide. The hydrophobic material coated on the surface of lithium nickel cobalt manganese oxide is insoluble in water, so that the lithium nickel cobalt manganese oxide composite material solves the problem that the batteries using conventional lithium nickel cobalt manganese oxide materials easily absorb water. A method for preparing the lithium nickel cobalt manganese oxide composite material is also disclosed.