Abstract: The six reasons for deck sinking in floating roof tank are discussed from the point view of construction and operation, and four countcrmcasures presented accordingly. The countcrmeasures include: ①never blow purging gas into tank and run the. tank agitator periodically; ②check, at regular intervals, the single deck plate and the scaling mechanism for any leakage and damage; ③frequently check the drain pipe for leakage, especially when the accumulated water comes upto a certain level; and ④install an external float gauge in the floating roof tank so that operator can keep informed on the deck's condition and the liquid level.