An LNG storage tank comprises a heat insulating wall on an inner surface of the storage tank, a sealing wall contacting LNG on the heat insulating wall, and a structure to support the sealing wall. The structure comprises an anchor structure, which comprises an anchor member between the inner surface of the storage tank and the sealing wall to secure the sealing wall to the inner surface, and a heat-insulating material around the anchor member. The anchor member is coupled at several portions to the inner surface. The structure provides a simple configuration to the heat insulating wall and the sealing wall, and a simple connection therebetween, enabling convenient construction thereof while increasing sealing reliability. The structure simplifies an assembled structure and a manufacturing process, reducing a construction time of the tank while efficiently relieving stress on the tank.