Abstract: The bolt holes of eight drum filters in CNNO Qinshan Phase Ⅱ power plant elongate（like ellipse） and get bigger with varying degrees,which cause the intensity of drum filter structure sharply declines,and the risk of failure occurs at any time.The analysis reveals that the galvanic corrosion and bolt loose are the root causes that result in the elongating and enlarging of the bolt holes of drum filer.The analysis concludes that the overall corrosion resistance of the drum filter hub and combined inspection methods of fasteners can eliminate the hidden trouble of elongation and enlargement of the bolt holes of drum filter hub,and effectively improve the operation reliability of the drum filters.