Abstract: The wire at the T－shaped clamp of a certain 330 kV transmission line broke. The causes of wire fracture were studied using methods such as macroscopic observation, chemical composition analysis, size measurement, metallographic examination, tensile testing and scanning electron microscopy analysis. The results show that the deformation degree of the crimping area was too small, resulting in insufficient clamping force of the crimping joint. The inner wall of the crimping joint did not fully contact the aluminum wire, so the diversion area was too small. During operation, the temperature of the contact area increased, and the surface of the aluminum wire was burned and damaged. When the load on the line increased, the local temperature of the line further increased, and the tensile strength of the wire decreased significantly, ultimately causd the wire inside the clamp to break.