In order to prevent fire accidents from occurring in the case of external floating roof tank exposed to a lightning strike or thunder and lightning induction, it is necessary to adopt a structure which can prevent thunder and lightning strike in external floating roof tank sealing system. Analyzed is the sealing structure of external floating roof tank, it is found that tranditional external floating roof tanks have such a sealing structure as primary seal (elastomer seal) and secondary seal and combustible gas exists between the primary and secondary seals, which will have high probability of fire and explosion in case of a lightning strike. For this reason, it is very necessary to optimize and improve the sealing structure of tranditional external floating roof tank. Through reforming the existing seal structure, canceled is the conducting electrostatic piece, added is the equiptential bounding conductor and used is the inert gas capsule to fill the interspace between the primary and secondary seals and space in the floating tray. The improvement of the sealing system in external floating roof tank can effeciently control some potential safety hazard.