The present invention provides a preparation method of a high-temperature furnace hardening insulation material, and the method comprises the following steps: first, cutting carbon fiber to obtain short fiber and long fiber, and evenly mixing the short fiber and the long fiber to obtain mixed fiber; second, evenly mixing a dispersant and water to obtain a dispersion liquid; third, evenly mixing the liquid dispersion and the mixed fiber to obtain a slurry; fourth, molding the slurry by first vacuum suction filtration to obtain a blank material, pouring an adhesive onto the blank material, and molding the blank material by second vacuum suction filtration to obtain a molded product; fifth, curing; sixth, performing carbonization-high temperature treatment to obtain the high-temperature furnace hardening insulation material. The high-temperature furnace hardening insulation material prepared by the method has low density, low thermal conductivity, high mechanical strength and other characteristics, can be widely used as an insulation material in crystalline silicon high-temperature furnaces, vapor deposition furnaces, ceramic sintering furnaces and other high temperature furnaces.