Abstract: In a 110 kV transmission line, cracking failure of the tower leg angle steel occured during the infrastructure installation. The causes of cracking of the tower leg angle steel were analyzed by macroscopic test, chemical composition analysis, mechanical property test, metallographic test, fracture analysis, finite element analysis and so on. The results show that the punching technology of the bolt hole of the tower leg angle steel was not appropriate, and more cracks formed at the edge of the bolt hole. Under the overload stress formed by the abnormal prebias load during the installation of the tower, the cracks at the edge of the bolt hole expanded and caused cracking failure of the angle steel. Finally, corresponding prevention and control measures were proposed.