The invention relates to the thermal design field of high thermal conductivity, in particular to a preparing method of a high thermal conductivity device. The preparing method includes the steps that (1) at least five graphite films are prepared with polyimide as a precursor; (2) starting from one end of each graphite film in the at least five prepared graphite films, the contact surface between every two adjacent graphite films is uniformly coated with heat conductive glue to form at least five composite graphite films, and the thickness of a glue layer is 10 micrometers; (3) the upper surface and the lower surface of the at least five composite graphite films in the step (2) are compounded with high molecular material films with the thickness of 25 micrometers through heat conductive glue to form a composite graphite film; (4) the composite graphite film in the step (3) is placed in a metal mold, and vacuumizing pressurization and standing curing are carried; (5) a composite graphite film is obtained again by repeating the steps (1)-(4), the two composite graphite films are compounded through adhesive and put into the metal mold to conduct vacuumizing pressurization and standing curing, and the high thermal conductivity device is obtained.