Abstract: Taking BEPCII superconducting RF (SRF) cavity as an example, this paper analyzes several common causes of the SRF cavity failure, including hardware failure of RF system, beam loss and mechanical failure of the tuner, by combining theoretical calculation and experimental observation of the main RF parameters such as the cavity voltage, the input power and the tuning angle, etc. It focuses on the SRF failure caused by the abnormal motion of the tuner. These analyses provide an important reference for reducing BEPCII RF system faults and increasing the operational reliability of BEPCII.