A cable tie tool has a first operating unit, a second operating unit, a pivoting shaft, a torsion spring, a cutting assembly, and an extension spring. The second operating unit has two guiding holes aligned to each other. The pivoting shaft is mounted in the guiding holes, is pivotally connected the first and the second operating units, and is movable along the guiding holes. The torsion spring abuts against and pushes the first and the second operating units. The cutting assembly has an activating element pivotally connected to the second operating unit and a cutting element movably mounted in the second operating unit and driven by the activating element. The extension spring is connected between the activating element and the second operating unit. When the extension spring is stretched, the activating element blocks the pivoting shaft from moving along the guiding holes.