The invention provides a centering and clamping device for a multi-diameter pipe. The device comprises a rack end cover, a rocker, a motor, a motor base, a rack, a connecting block, a sliding block vertical column, a movable sliding block, a screwing-in sliding frame, a transmission gear, a rotating shaft frame, a motor gear, a motor shaft, a threaded rod, a fixing nut, a ball bearing and a shaftsleeve, wherein the rack end cover is arranged on the right side of the upper part of the rack through bolts; the rocker is clamped at the right end of the threaded rod, and the motor is welded to theupper part of the motor base. The motor drives the motor gear to rotate, the rotating shaft frame is rotated through gear transmission, the movable sliding block and the screwing-in sliding frame aredriven to rotate synchronously, and the pipe rotates along with the movable sliding block and the screwing-in sliding frame; the simple structure is used, so that clamping and centering of pipes withdifferent diameters are achieved in the actual operation process, the rotating speed during pipe machining is adjusted, the tool cost is reduced, and the quality and machining efficiency of the outersurface of the pipe are improved.