Abstract: Aiming at the fracture event of Z-10 four-legged right-angle hanging plate of a 220 kV line, this paper systematically reveals its fracture mechanism through operating environment analysis, accurate load calculation, structural dimension inspection and finite element simulation. The results show that the manufacturing defect of insufficient plate thickness is the inducement, while the long-term fatigue failure caused by the coupling of dead weight, wind load and icing load is the root cause. This paper expounds the common hidden danger of insufficient safety margin of this type of hanging plate under specific working conditions, and puts forward some specific preventive measures such as changing fitting models, strengthening monitoring and optimizing design standards.