Abstract: The failure of the safety shaft coupling in a typical aero-engine occurred now and then during testing and service, which had a serious impact on the safe use of the engine. In the present work, the working principles of the safety shaft coupling was described and the fault tree for the fractured safety shaft coupling was established to analyze the probable causes for the failure of the safety shaft coupling. It is assumed that the main causes for the failure of safety shaft coupling include improper design, lower machining accuracy, and assembly deviation. Finally, some proper measures was put forward for the failure. The above results are important to dealing with such failure.