The invention discloses a 
steel bar bending mechanism applied to an automatic hoop bending 
machine. The mechanism comprises a rotating motor and a bending head capable of rotating in the circumferential direction driven by the motor, and a movable bending rod is detachably mounted on the bending head; a 
steel bar positioning part is detachably installed on the bending head, beside the movable bending rod, and a 
steel bar positioning groove is formed in the middle of the steel bar positioning part; a vertically arranged hollow outer shaft is fixedly installed under the bending head, the hollowouter shaft can rotate driven by a bending motor, and drive the movable bending rod to rotate synchronously, steel bars protruding out of the steel bar positioning groove are bent at a set angle, andwhen bending, the end, close to the movable bending rod, of the steel bar positioning part forms a steel bar 
abutment part; the mechanism also comprises a second 
telescopic cylinder, and through starting the second 
telescopic cylinder, the hollow outer shaft and the bending head can be driven to expand and contract up and down; the hollow outer shaft sleeves an inner telescopic shaft, and the steel bar positioning part and the inner telescopic shaft can expand and contract up and down driven by a first 
telescopic cylinder.