An insulating wall fixing device for liquefied natural gas storage tanks, wherein the insulating wall fixing device is configured to mutually couple primary and secondary insulating walls of a liquefied natural gas storage tank, the primary insulating wall being placed on top of the secondary insulating wall, the insulating wall fixing device comprising: a base socket; and a securing stud inserted into the base socket, wherein the base socket is formed on an upper surface thereof with an insertion hole through which the securing stud is inserted into the base socket and has an interior space in which one end of the securing stud is settled; the base socket is configured to be securely inserted into a groove formed in a top plywood of the secondary insulating wall, and the base socket has an outwardly protruding lower portion to have a stepped cross-section to be securely inserted into a stepped groove formed in the top plywood of the secondary insulating wall; wherein the securing stud comprises an insertion portion inserted into the interior space of the base socket through the insertion hole, a fastening portion protruding from the insertion portion outwardly of the base socket and a disk-shaped seated portion outwardly protruding along a circumference of the fastening portion, the insertion portion having a spherical shape and comprising multiple leg members divided by a groove formed from one end of the insertion portion to the other end of the insertion portion; the multiple leg members of the insertion portion are retracted toward the groove to enter the insertion hole upon inserting the securing stud into the base socket; and an end of the disk-shaped seated portion configured to be welded to secondary sealing wall and an end of the disk-shaped seated portion being seated on an upper surface of the base socket. a base socket; and a securing stud inserted into the base socket, wherein the base socket is formed on an upper surface thereof with an insertion hole through which the securing stud is inserted into the base socket and has an interior space in which one end of the securing stud is settled; the base socket is configured to be securely inserted into a groove formed in a top plywood of the secondary insulating wall, and the base socket has an outwardly protruding lower portion to have a stepped cross-section to be securely inserted into a stepped groove formed in the top plywood of the secondary insulating wall; wherein the securing stud comprises an insertion portion inserted into the interior space of the base socket through the insertion hole, a fastening portion protruding from the insertion portion outwardly of the base socket and a disk-shaped seated portion outwardly protruding along a circumference of the fastening portion, the insertion portion having a spherical shape and comprising multiple leg members divided by a groove formed from one end of the insertion portion to the other end of the insertion portion; the multiple leg members of the insertion portion are retracted toward the groove to enter the insertion hole upon inserting the securing stud into the base socket; and an end of the disk-shaped seated portion configured to be welded to secondary sealing wall and an end of the disk-shaped seated portion being seated on an upper surface of the base socket.