Tire building drum

The invention provides a t tire building drum which comprises two half drums. Each half drum comprises a tire ring locking unit, a reverse packing unit located on the outer side in the axial directionof the tire ring locking unit and a contraction area segment located on the inner side in the axial direction of the tire ring locking unit. Each contraction area segment comprises a body, an annularcontraction area which is arranged outside the body in a sleeving manner and can do in the radial direction, an actuating assembly contained in the body and multiple supporting sheet sets, wherein the multiple supporting sheet sets are evenly distributed along the circumference, and the actuating assembly drives the multiple supporting sheet sets to form a supporting face, so that the annular contraction face is at the flushing or contraction position. Each actuating assembly comprises multiple stop parts, and grooves are formed in the stop parts. In the contraction positions, the supportingsheet sets are connected wi