Abstract: Combining with the cracking failure event of lightning rod flange, the causes of cracking failure of lightning rod flange are analyzed and summarized. Firstly, the macroscopic and microscopic morphology of the cracking fracture is observed. Secondly, the cracking failure of the lightning rod flange is detected through methods of nondestructive testing, chemical composition analysis, mechanical property analysis and metallographic examination. The results show that under the combined action of average wind load and fluctuating wind load, the lightning rod is in a swinging state for a long time. Due to the influence of structural steel, the lower flange of the lightning rod is subjected to the alternating bending stress, and there are welding defects such as incomplete fusion, covering and undercut at the fillet weld, which would lead to serious stress concentration and cracking. Finally, the corresponding preventive measures and suggestions are put forward based on this failure analysis.