The invention discloses a dismounting device for an aero-engine high-pressure combined rotor. The dismounting device comprises a first fixing mechanism, a second fixing mechanism and a force applying mechanism, wherein the first fixing mechanism is used for fixing a high-pressure turbine rotor component of a high-pressure combined rotor on a first end face of an engine cast; the second fixing mechanism is used for fixing a high-pressure shaft of the high-pressure combined rotor on a second end face of the engine cast; the force applying mechanism is used for penetrating through the first fixing mechanism along an axial direction of the high-pressure combined rotor and is connected with a gland nut of the high-pressure combined rotor so as to dismount the gland nut in the manner of twisting; the first fixing mechanism is used for fixing the structure of the high-pressure turbine rotor component, so as to prevent the high-pressure turbine rotor component from being influenced by the dismounting of the gland nut and rotating along circumferential direction; the second fixing mechanism is used for fixing the structure of a high-pressure shaft, so as to prevent the high-pressure shaft from being influenced by the dismounting of the gland nut and rotating along circumferential direction; the condition that the aero-engine high-pressure combined rotor meets the assembling technical requirement without influence on the surrounding part structures can be guaranteed.