Abstract: An analysis was conducted on the causes of fracture and detachment of a 110 kV cable terminal cast aluminum tail tube, and the influence of porosity defect on the overall performance of the tail tube was investigated. Through technical methods such as chemical composition analysis, mechanical performance testing, and scanning electron microscopy, the accident causes were discussed from multiple perspectives, considering factors such as material, structure, and operating conditions.Numerous pore-type defects were identified in the faulty tail tube, along with material composition segregation. The results indicated that the fracture occurred at the transition corner of the tail tube flange, which is the location with the largest cross-sectional change in the connection between the cable terminal and the gas insulated switchgear (GIS). Micro-cracks initiated at the edges of the pore defects due to the notch effect and propagated under alternating loads such as those induced by GIS electromagnetic force. Moreover, the inhomogeneous material composition led to an overall decline in comprehensive mechanical properties. During long-term operation, cracks first developed at the tail tube corner, where stress is most concentrated, resulting in insulation breakdown of the tail tube. Under the impact of arc voltage accompanied by sustained short-duration fault current, a overall brittle fracture ultimately occurred, leading to detachment.