The invention discloses a hydraulic tensioning method for fixing a gear. The method comprises the following steps that firstly, clamp fixing is carried out, and a clamp penetrates through a through hole in the middle of the gear; secondly,
hydraulic pressure output is carried out, a hydraulic
machine outputs
hydraulic pressure to enable the clamp to move or rotate, and therefore the clamp in the through hole in the middle of the gear to shift, the gear is tensioned, and the gear can be machined conveniently; thirdly, hydraulic resetting is carried out, after
machining is completed, hydraulic resetting is carried out, the clamp moves or rotates reversely, and therefore the clamp in the through hole in the middle of the gear is reset to an initial state; fourthly, a workpiece is taken out, and the machined workpiece is taken out. According to the method, the clamp moves or shifts through the
hydraulic pressure, and therefore the gear is tensioned, the output hydraulic pressure is ingeniously converted into tensile force, the gear is tensioned in the through hole in the middle of the gear, the conception is ingenious, the structure is reasonable, and excessive
machining due to the fact that the fixing clamp clamps the gear due to vibration can be avoided.