The invention discloses a thermal bulging method for an aluminum alloy special-shaped ring-rolled piece. The method comprises the following steps of: assembling a hot-rolled aluminum alloy special-shaped ring-rolled piece on the periphery of a preheated bulging block in a bulging machine, and starting the bulging machine to make the bulging block extrude the ring-rolling piece radially from the inner circumferential surface of the ring-rolled piece to finish first bulging, wherein the bulging temperature is 350-410 DEG C, the bulging time is 15-20 seconds, the dwelling time is 11-14 seconds, and the deflection is 0.4-0.8 percent; rotating the ring-rolled piece by 45 degrees along a central axis to finish a first rotation; performing second bulging according to the operation above, wherein the bulging temperature is 300-370 DEG C, the bulging time is 20-30 seconds, the dwelling time is 16-18 seconds, and the deflection is 0.5-1.1 percent; rotating the ring-rolled piece once according to a first rotating direction to finish second rotation; and performing third bulging according to the operation above, wherein the bulging temperature is 270-330 DEG C, the bulging time is 30-40 seconds, the dwelling time is 25-28 seconds, and the deflection is 0.5-1.1 percent. The size accuracy of the bulged ring-rolled piece can be up to 1-2 per thousand of a corresponding size; and the aluminum alloy special-shaped ring-rolled piece is manly applied to the fields of aerospace and the like.