The invention discloses a lithium titanate/graphene composite cathode material for a lithium ion battery. The composite cathode material is obtained by mixing lithium titanate and graphene oxide and then performing reduction by a reducing agent. A preparation method of the composite cathode material comprises the steps of preparing pure-phase lithium titanate by a hydrothermal method, sufficiently mixing pure-phase lithium titanate and graphene oxide, adding an appropriate amount of reducing agent, and shifting pure-phase lithium titanate, graphene oxide and the reducing agent to a reaction kettle to react for a certain time at a certain temperature to obtain the lithium titanate/graphene composite cathode material. The method synthesizes the lithium titanate/graphene composite material by an industrially extensively used hydrothermal reaction, so that the method is simple to operate and low in equipment requirement, and is suitable for industrial production; and the prepared lithium titanate/graphene composite material has higher specific capacity, good high rate performance and excellent cycle performance, and is applicable to the fields of portable electronic equipment, electromobiles, energy storage equipment and the like.