The invention discloses a deep hole boring tool which comprises a taper shank inserted into a machine tool, a stepped shaft, a boring bar and a blade, wherein the stepped shaft is arranged at the lower end of the taper shank; the lower end of the stepped shaft is provided with the boring bar; the blade is arranged at the lower part of the boring bar; the lower end of the stepped shaft is provided with two cylinders which are in bilateral symmetry; a stabilizing block is connected to the lower end of each cylinder and can be controlled to move up and down by the cylinder; the stepped shaft is provided with a limit tray which is used for supporting the stabilizing blocks after the cylinders are opened; and the radius of the limit tray is smaller than that of the blade. According to the deep hole boring tool, the stabilizing blocks are arranged on the boring bar and can be controlled to move up and down by the cylinders, so that the excursion of the boring bar in the machining process can be reduced, the accuracy of the machined holes is high, and the quality of the machined products is improved.