The invention discloses an oil tank sealing device and a use method thereof. The oil tank sealing device comprises a first pipe body, a first sealing cover body, a second sealing cover body and an opening-closing device. The first pipe body comprises a containing cavity; the first sealing cover body is used for forming a seal with the bottom of the containing cavity, and the first sealing cover body is hinged to the side wall of the first pipe body; the second sealing cover body is arranged above the first sealing cover body and used for forming a seal with the containing cavity formed in the second sealing cover body, and a first sealing hole is formed in the second sealing cover body; and the opening-closing device is used for sealing the first sealing cover body or enabling the sealing cover body to be separated from the bottom of the containing cavity. According to the oil tank sealing device and the use method thereof, after an original oil pump in an oil tank loses efficacy, continuous lightering can be conducted on storing oil in the oil tank through the mode that an oil pump is additionally arranged, and when the oil tank is in the process of oil pump additional arranging, the problem of oil gas leakage in the oil tank can be effectively prevented.