Abstract: Generally, large-scale floating-roof oil tank works with the secondary seal, however, where exists a space from light gas to blast inducedby lightning stroke, or fire accident. Lightning theory indicates that conducting strip of secondary seal is attached by external elastic forceinstead of continuous and reliable electrical connection, which has the probability of spark discharge when the lightning current is flowing through the conducting strip. The result of lightning risk experiment applying 8/20 μs impulse current wave shows that the more reliable connection between conducting strip and tank wall is, the more difficult for lightning striking is. The oil dirt may control the appearance of spark to a certain degree, but lightning current may still pass through the conducting strip and produce spark discharge for the shortage of insulation function. When lightning current passes through the conducting strip, only several hundreds ampere of current can cause spark discharge. Based on the above conclusions, the proposed measures are presented, which acts as the guidance function to ensure the safety operation of large-scale floating-roof oil tank against lightning.