The invention discloses thermal conductive plastic applying a modified carbon material, and a preparation method thereof. The thermal conductive plastic comprises the following components in percentage by mass: the modified carbon material, magnesium oxide, boron nitride, nylon 66, a polyanionic type high polymer, a dispersing agent, and a couplant, wherein the modified carbon material comprises the following components in parts by weight: a base carbon material, a surfactant, a polycationic type high polymer, and a couplant; the modified carbon material is prepared by the steps of: mixing water, the base carbon material, sodium chloride, the surfactant and the couplant according to a proportion and then performing ultrasonic treatment, slowly adding the polycationic type high polymer during the ultrasonic process, continuously performing ultrasonic treatment and then stirring for 20-24h, filtering and drying. According to the thermal conductive plastic applying the modified carbon material, and the preparation method thereof, the problem that the materials inside the plastic are mixed unevenly can be effectively solved, and the compatibility of the carbon material can be improved greatly; the dispersity of the whole material mixture can be enhanced, and plugging is difficult in the extrusion process; the synthetic technology is simple, and the conditions of high temperature, a strongly corrosive environment and the like are not required.