Abstract: Aiming at the fracture of iron fittings in 330 kV transmission line towers, and combining with the nondestructive testing and physical and chemical testing methods, the real causes of the iron fittings fracture in towers are comprehensively analyzed by means of macroscopic examination, fracture inspection, structural size measurement, chemical composition analysis, hardness inspection, mechanical property test, metallographic examination, scanning electron microscope fracture and energy spectrum analysis. It is found that the samples of iron fittings had obvious plastic deformation before fracture, and the fracture occurred in the weak parts of bolt holes in tower materials, and the section was characterized by ductile fracture. Before the fracture, the iron accessory sample bears a great bending and torsion stress, which exceeds the bearing capacity limit of the material, resulting in the deformation and cracking of the stress concentration part of the screw hole, which leads to the overturning of the whole iron tower. Reference measures and suggestions are put forward, which would provide a scientific basis for the next comprehensive investigation, treatment and prevention of hidden dangers of the similar problems.