A liquefied natural gas, LNG, storage tank , including an opening portion (H) formed at an inner hull disposed on an upper side of the LNG storage tank , and a pump tower having a plurality of pipes (P) and installed through the opening portion (H), the plurality of pipes (P) is uprightly installed in a direction passing through an upper surface of the storage tank , wherein said LNG storage tank further comprises a pump tower installation structure, said pump tower installation structure comprising: an adaptor configured to be disposed at a predetermined area (S1) of the opening portion (H) ; and a cover having through-holes corresponding to the pipes of the pump tower and is configured to be disposed at a remaining area (S2) of the opening portion (H) to be connected with the adaptor , said cover supporting the pipes (P) while closing the opening (H), wherein the cover further has a cover insulation board provided under the cover and formed under the opening portion (H), a peripheral portion of the cover insulation board formed downward from the opening (H) is insulated, the pump tower installation structure further comprising: an insulation layer configured to be disposed between the cover insulation board of the cover and a lower insulation board of the LNG storage tank which are respectively provided under the inner hull , a vertical closing portion vertically bonded under the adaptor and the cover to be in contact with the insulation layer , and an adjustment closing portion fixedly bonded to the vertical closing portion so as to adjust a height thereof and to be disposed on the same plane with the insulation layer . an adaptor configured to be disposed at a predetermined area (S1) of the opening portion (H) ; and a cover having through-holes corresponding to the pipes of the pump tower and is configured to be disposed at a remaining area (S2) of the opening portion (H) to be connected with the adaptor , said cover supporting the pipes (P) while closing the opening (H), wherein the cover further has a cover insulation board provided under the cover and formed under the opening portion (H), a peripheral portion of the cover insulation board formed downward from the opening (H) is insulated, the pump tower installation structure further comprising: an insulation layer configured to be disposed between the cover insulation board of the cover and a lower insulation board of the LNG storage tank which are respectively provided under the inner hull , a vertical closing portion vertically bonded under the adaptor and the cover to be in contact with the insulation layer , and an adjustment closing portion fixedly bonded to the vertical closing portion so as to adjust a height thereof and to be disposed on the same plane with the insulation layer . an insulation layer configured to be disposed between the cover insulation board of the cover and a lower insulation board of the LNG storage tank which are respectively provided under the inner hull , a vertical closing portion vertically bonded under the adaptor and the cover to be in contact with the insulation layer , and an adjustment closing portion fixedly bonded to the vertical closing portion so as to adjust a height thereof and to be disposed on the same plane with the insulation layer . <EOS>