Provided are a composite material and a preparation method thereof, a negative electrode material, and a lithium ion battery. The negative electrode material includes at least one composite material, and the lithium ion battery includes at least one composite material. The composite material has a core-shell structure composed of an inner core and a hydrophobic coating layer, with the inner core including at least one lithium-containing silicon oxide, and the hydrophobic coating layer being used to cover the inner-core material.