The invention discloses carbon nano tube/expanded graphite combined padding and a preparing method thereof as well as a heat conducting high polymer material containing the combined padding and a preparing method of the heat conducting high polymer material. The combined padding is prepared by premixing 1-100 parts of carbon nano tube and 100 parts of expanded graphite by a high speed mixer then heating by placing into a high temperature furnace; the heat conducting high polymer material is prepared by premixing 1-100 parts of the combined padding, 100 parts of plastic matrix, 0.5-10 parts of coupling agent, 0.5-5 parts of lubricating agent and 0.5-5 parts of antioxidant by the high speed mixer, and then placing in melting blending equipment for melting and mixing. The preparing process is simple, and the prepared combined padding and heat conducting high polymer material have well heat-conducting property and have very good application prospect.