Abstract: The main transformer bushing performs insulation and current diversion functions, and directly affects the safe operation of the unit. Currently, the epoxy resin-based glass fiber dry-type bushings used in 220 kV and below large-capacity transformers have extremely high failure rates in the conical part. The root cause of the failure is the gradual development of local discharge in the capacitor screen to breakdown. The causes include concentrated field strength, improper design matching, and manufacturing defects. The fault is highly concealed and cumulative, and is prone to causing unplanned outages. This study based on the failure case of a generator unit, analyzes the faults of this type of bushing from multiple dimensions and proposes a comprehensive measure of “optimizing production design+monitoring of the energized grounding lead-out line at the end of the bushing”, which can provide reference for the safe operation of similar transformers.