Abstract: The structure of wind turbine generator system (WTGS) is briefly introduced, and the structural parts that often fail on WTGS, as well as their materials, heat treatment process and failure modes were summarized. The high-strength bolts with a large number of applications and important functions on WTGS were selected as the main content of this lecture. The application characteristics, failure characteristics, structural characteristics, force characteristics and failure causes of the bolts on WTGS were discussed in detail. Combining years of failure analysis experience, actual cases were used to focus on the two most common failure types of the bolts on WTGS-fatigue fracture and hydrogen embrittlement fracture, and the root causes of the two failure were analyzed. Finally, preventive measures to avoid failure of bolts on WTGS were put forward.