The invention discloses a multi-section deep hole drill, and belongs to the technical field of drilling tools. The multi-section deep hole drill comprises a gear carrier, a controller, a supporting plate, supporting rods, a first sliding rail, first sliding blocks, struts, a second gear, linear motors, moving blocks, a second motor, a transparent cover, a first drill rod, second sliding rails, second sliding blocks, a first air cylinder, a machine barrel, a first gear, a first motor, a support, a third sliding rail, third sliding blocks, sleeves, fourth drilling rods, drills, second air cylinders, second drilling rods, a double-head air cylinder and a groove. The support is installed at the right side of the supporting plate. The first motor is installed beneath the support, and the first gear is installed on an output shaft of the first motor. The second gear is installed at the left side of the first gear. The second gear is installed on the gear carrier. The first gear and the second gear are engaged with each other. The gear carrier is installed beneath the supporting plate. The two supporting rods are installed beneath the supporting plate. The first sliding rail is installed beneath the supporting rods. The first sliding rail is provided with the two first sliding blocks. The multi-section deep hole drill has the advantage that the machining hole diameter can be changed.