A ground liquefied natural gas storage tank comprising: an independent tank in which a space for storing a storage material is formed to constitute an inner tank, a heat insulation structure, wherein the independent tank is located over the heat insulation structure configured to be installed on the ground; configured to be installed on the ground; at least one sandwich plate configured to be modularized and manufactured to comprise a pair of metal plates facing each other, the metal plates having a reinforcing material formed therebetween, and a filler filled between the metal plates, wherein the at least one sandwich plate is configured to surround the outer surface of the independent tank to constitute an outer tank, wherein the outer tank comprises the at least one sandwich plate, an outer tank roof and an outer tank slab; an external reinforcing member formed on an outer surface of a wall body of the at least one sandwich plate, wherein the external reinforcing member comprises a first longitudinal reinforcing member and a second lateral reinforcing member configured at a right angle to the first longitudinal reinforcing member; characterized in that a further external reinforcing member is formed on an outer surface of the tank roof, wherein said external reinforcing member comprises a third longitudinal reinforcing member and fourth and fifth reinforcing members (24, 25) configured at a right angle to the third longitudinal reinforcing member and connected to the first longitudinal reinforcing member and the second lateral reinforcing member; and in that the gas storage tank further comprises an external reinforcing member formed on the outer tank slab, wherein the external reinforcing member comprises sixth and seventh reinforcing members (26, 27) configured at right angles to each other and connected to the first longitudinal reinforcing member and the second lateral reinforcing member. an independent tank in which a space for storing a storage material is formed to constitute an inner tank, a heat insulation structure, wherein the independent tank is located over the heat insulation structure configured to be installed on the ground; configured to be installed on the ground; at least one sandwich plate configured to be modularized and manufactured to comprise a pair of metal plates facing each other, the metal plates having a reinforcing material formed therebetween, and a filler filled between the metal plates, wherein the at least one sandwich plate is configured to surround the outer surface of the independent tank to constitute an outer tank, wherein the outer tank comprises the at least one sandwich plate, an outer tank roof and an outer tank slab; an external reinforcing member formed on an outer surface of a wall body of the at least one sandwich plate, wherein the external reinforcing member comprises a first longitudinal reinforcing member and a second lateral reinforcing member configured at a right angle to the first longitudinal reinforcing member; characterized in that a further external reinforcing member is formed on an outer surface of the tank roof, wherein said external reinforcing member comprises a third longitudinal reinforcing member and fourth and fifth reinforcing members (24, 25) configured at a right angle to the third longitudinal reinforcing member and connected to the first longitudinal reinforcing member and the second lateral reinforcing member; and in that the gas storage tank further comprises an external reinforcing member formed on the outer tank slab, wherein the external reinforcing member comprises sixth and seventh reinforcing members (26, 27) configured at right angles to each other and connected to the first longitudinal reinforcing member and the second lateral reinforcing member.