The seal of quick opening blind plate of the three sets of the same type of feed gas separator (F-020701-1/2/3) in a gas gathering station of a high sour gas field failed in the air tightness test during the major maintenance shutdown. Through on-site mapping and inspection, taking into account its sealing principle, fault tree analysis was performed. It was concluded that the change of sealing structure due to corrosion in a hydrogen sulfide environmental was the root cause of sealing failure. The repair method adopted on site was machining the sealing structure after weld overlay of the corroded and thinned surface of the sealing structure was carried out. After the repair, the seal passed both air tightness test and helium nitrogen test to demonstrate that the equipment could be put into operation production after the shutdown.It is concluded that the unit can realize the recovery of sealing structure.