The invention provides a tire unloading device for a tire building machine, which is used for forwards or backwards unloading green tires to be built. The tire unloading device comprises a horizontal shifting support frame, an automatic tire unloading mechanism arranged on one side of the support frame and a control assembly, wherein the automatic tire unloading mechanism comprises a depressing part arranged at the upper part of the support frame and a holding part arranged at the lower part of the support frame, and at least one of the depressing part and the holding part can shift up and down to grip or loosen a green tire to be built; the holding part comprises a bearing plate with up and down rotatable front and back ends, at least two holding paws pivoted with the front and back ends of the bearing plate, and a tire unloading driving assembly for driving the bearing plate to rotate; and when the automatic tire unloading mechanism is in a tire unloading state, the tire unloading driving assembly drives the bearing plate to rotate and causes the bearing plate to tilt forwards or backwards, thereby guiding the green tire to be built to be unloaded forwards or backwards.