The invention relates to a milling tool for steam turbine bacterial-type root blades, and solves the problem in the prior art that no special milling tool for processing the steam turbine bacterial-type blade root blades exists. A positioning block is vertically and fixedly connected with the middle part of one end of an upper end surface of a base plate in the width direction; a support screw passes through a first threaded hole and is in threaded connection with a pressing plate; two sides of the base plate, along the axial direction of a positioning threaded hole, are respectively fixedly connected with an ejection rod support and a support screw sequentially; a screw rod passes through the positioning threaded hole of the positioning block and is connected with a positioning thread; the lower ends of the bacterial-type root blades are clamped on the positioning block for positioning; the screw rod is rotated so as to butt against the bacterial-type root blades; each pressing plate is pressed on the upper surfaces of the bacterial-type root blades; adjusting studs are arranged in a manner of penetrating through guide grooves of the pressing plates; a nut is threadedly connected with the upper end of each adjusting stud so as to press the corresponding pressing plate tightly; and the threaded ejection rods are rotated so as to push two sides of the bacterial-type root blades tightly. The milling tool for the steam turbine bacterial-type root blades, provided by the invention, is used for clamping the steam turbine bacterial-type root blades.