An electric tightening head for tightening a lock nut of a single through shaft, comprising a supporting plate (1), sliding blocks (2), tightening jaws (3), springs (4), wedged pad irons (5), wedged pad iron connecting arms (6), a pulling rod (7), an initial position detecting bolt (8) and stop bolts (9), wherein the supporting plate (1) is connected with the sliding blocks (2), the tightening jaws (3) and the pulling rod (7); the springs (4) are connected with the stop bolts (9) mounted on the tightening jaws (3); the tightening jaws (3) are connected with the wedged pad irons (5); the wedged pad irons (5) are connected with the wedged pad iron connecting arms (6); and an upper end of the pulling rod (7) is connected with the initial position detecting bolt (8).