The invention discloses a method for preparing high-thermal-conductivity graphite films. The method includes the steps of (1), dissolving a diamine monomer into an organic solvent under the protection of nitrogen, adding a dianhydride monomer A and reacting so as to obtain a low-viscosity polyamide acid prepolymer; (2), adding waterborne carbon black into the low-viscosity polyamide acid prepolymer obtained in the step (1), and stirring and ultrasonically dispersing evenly; (3), adding a dianhydride monomer B into the polyamide acid prepolymer obtained in the step (2), and reacting so as to obtain modified polyamide acid resin; (4), coating the modified polyamide acid resin with wet films by means of curtain coating, and conducting imidization so as to obtain modified polyimide films; (5), stacking the modified polyimide films crossly, and sequentially putting the modified polyimide films into a carbonization furnace and a graphitization furnace for carbonization and graphitization so as to obtain the high-thermal-conductivity graphite films. The high-thermal-conductivity graphite films prepared by the method are high in thermal conductivity and excellent in tensile strength.