Abstract: The breakdowns have happened many times to an airplane engine as a result of the break of a taper gear. In order to find the reason, modal analysis was performed and twodiameter-nodes modal fatigue test on the gear was conducted on a shaker. The breakdown reappearance was realized. Erperimental data were collected which Provide an important basis for analyzing breakdown mechanism of the gear and enable a research methed for vibration design of the same kind of gears.