The invention discloses an expansion type centered clamping and milling device, and belongs to the technical field of machines. The expansion type centered clamping and milling device comprises a locking nut, a spring box, a mandrel, a reset spring, a spring seat plate, a clamp body, a bearing sleeve, a positioning supporting plate, a steel wire and a pneumatic assembly; the mandrel penetrates the spring box; the reset spring is mounted in the spring box, the end, pointing to the pneumatic assembly, of the reset spring is connected with the spring seat plate, the clamp body is located between the spring box and the pneumatic assembly, the bearing sleeve is mounted on the clamp body, and guide grooves which are evenly formed in the radial direction are formed in the bearing sleeve, and the positioning supporting plate is mounted in the guide grooves of the bearing sleeve; the steel wire penetrates a mounting hole in the positioning supporting plate, and the bottom circular-arc slope of the positioning supporting plate makes contact with the conical face of the mandrel. Involute spline holes are adopted in the milling device for positioning, the structure is novel and simple, cost is low, centered clamping can be achieved, and the efficiency is high; and work is reliable, and automatic upgrading and reconstruction are facilitated.