An insulation wall fixing device for a liquefied natural gas storage tank, the LNG storage tank comprising: a primary insulation wall primarily insulating liquefied natural gas; a secondary insulation wall disposed under the primary insulation wall and secondarily insulating the liquefied natural gas, the secondary insulation wall comprising a secondary insulator and a secondary upper protective plate disposed on the secondary insulator; and a fixing device coupling the primary insulation wall to the secondary insulation wall, the fixing device comprising: a base socket and a stud coupled to the base socket, wherein the base socket has a lower circumference protruding in a step shape and a lower surface mounted on a groove formed on an upper surface of the secondary insulator; wherein the base socket comprising a socket body constituting a body of the base socket and a socket flange protruding in a step shape from the socket body; the socket body is inserted through a hole formed in the secondary upper protective plate, so that an upper surface of the socket body and an upper surface of the secondary upper protective plate are on the same plane; the socket flange is inserted into the space between the groove formed on the upper surface of the secondary insulator and the secondary upper protective plate to support a lower surface of the secondary upper protective plate; the stud includes a vane 321 protruding from a body of the stud and mounted on an upper surface of the socket body; a secondary sealing wall interposed between the primary insulation wall and the secondary insulation wall; the secondary sealing wall is welded to the vane in an adjoining region therebetween that is disposed on the upper surface of the socket body. a primary insulation wall primarily insulating liquefied natural gas; a secondary insulation wall disposed under the primary insulation wall and secondarily insulating the liquefied natural gas, the secondary insulation wall comprising a secondary insulator and a secondary upper protective plate disposed on the secondary insulator; and a fixing device coupling the primary insulation wall to the secondary insulation wall, the fixing device comprising: a base socket and a stud coupled to the base socket, wherein the base socket has a lower circumference protruding in a step shape and a lower surface mounted on a groove formed on an upper surface of the secondary insulator; wherein the base socket comprising a socket body constituting a body of the base socket and a socket flange protruding in a step shape from the socket body; the socket body is inserted through a hole formed in the secondary upper protective plate, so that an upper surface of the socket body and an upper surface of the secondary upper protective plate are on the same plane; the socket flange is inserted into the space between the groove formed on the upper surface of the secondary insulator and the secondary upper protective plate to support a lower surface of the secondary upper protective plate; the stud includes a vane 321 protruding from a body of the stud and mounted on an upper surface of the socket body; a secondary sealing wall interposed between the primary insulation wall and the secondary insulation wall; the secondary sealing wall is welded to the vane in an adjoining region therebetween that is disposed on the upper surface of the socket body. a base socket and a stud coupled to the base socket, wherein the base socket has a lower circumference protruding in a step shape and a lower surface mounted on a groove formed on an upper surface of the secondary insulator; wherein the base socket comprising a socket body constituting a body of the base socket and a socket flange protruding in a step shape from the socket body; the socket body is inserted through a hole formed in the secondary upper protective plate, so that an upper surface of the socket body and an upper surface of the secondary upper protective plate are on the same plane; the socket flange is inserted into the space between the groove formed on the upper surface of the secondary insulator and the secondary upper protective plate to support a lower surface of the secondary upper protective plate; the stud includes a vane 321 protruding from a body of the stud and mounted on an upper surface of the socket body; a secondary sealing wall interposed between the primary insulation wall and the secondary insulation wall; the secondary sealing wall is welded to the vane in an adjoining region therebetween that is disposed on the upper surface of the socket body.