A double-barner for a land-based liquefied gas storage tank and a method of constructing the same are disclosed. The double-barrier includes an insulating wall inside a tank body of the storage tank, and a sealing wall disposed inside the insulating wall to primarily prevent leakage of a liquefied gas while directly contacting the liquefied gas in the storage tank. The insulating wall includes a plurality of insulating panels attached to the tank body and separated from each other, and a space between the insulating panels is filled with an insulating material to secondarily prevent leakage of the liquefied gas. The double-barrier can doubly prevent leakage of the liquefied gas without additional installation of a secondary barrier outside the storage tank.