The invention relates to a tip-extension type deep hole boring cutter rod. A cutter seat (3) is positioned in a cavity between a press cover (1) and a gear installing seat (5), and a screw rod (11) connected with one end of a core shaft (10); a rack (6) is installed in a slot on one end of the core shaft (10); one inner edge of a cutter installing hole needs to be coincide with the symmetric center surface of double-row teeth; a cutter (2) is positioned in the cutter installing hole, and a tip is positioned on a center line of a processed hole; and gears (4) are respectively meshed with the double-row teeth of the rack and the cutter seat. The screw rod is rotated by rotating a handle (14) on the screw rod (11) to drive the core shaft (10) to move, and then the cutter tip is extended by the transmission among a thread pair, the rack, gears and the rack. When retracting, the tip enters the end part of an inner hole of a part; and when the tip extends out, the middle of the part is processed. By adopting a guiding block (9), the rigidity of the cutter rod is ensured, and the cutter rod is provided with axial scales and circumferential scales. The tip-extension type deep hole boring cutter rod is suitable for processing deep holes on both ends of a long-shaft part, wherein the deep holes have small inner diameters at two ends, large inner diameters in the middles and larger difference of diameter sizes.