Abstract: An analysis on the damage of flame arrester of oil tank has been made from its structure as well as daily care. Countermeasures against its disability have been presented, that is, casting the two semi-casing into one piece, leaving out the intermediat flanges, thickening the casing, and increasing the casting round-angle between the flanges and casing. In this way, the strength of casing can be enhance and local stress will be decreased. In addition, in order to enlongate the service life, the operating frequency of flame arrester should be properly reduced in daily care.