Abstract: In a routing inspection of a power company, the high-strength fastening bolts servicing for 4 years at the wind turbines pedestal were found fractured. After macrostructure inspection and scanning electron microscopy (SEM) analysis on the fracture, combining chemical compositions analysis, metallographic examination and hardness test to the bolt material, the fracture reason was discovered. The results show that the fracture was low stress and high cycle fatigue fracture. The severe surface decarburization produced during the quenching and tempering reduced surface hardness and strength of the bolt, accordingly, at the root of bolt where the stress concentrated, the cracks formed and constantly extended until fracture finally.