The invention discloses a fast die erecting device for a closed wall. A closed wall body is included. The fast die erecting device is composed of a vertical rod, a horizontal rod and an oblique rod, wherein the vertical rod, the horizontal rod and the oblique rod are connected with each other in a hinge manner, the vertical rod is vertically placed on a bottom plate of the closed wall body, the horizontal rod is fixed on the bottom plate of the closed wall body, the oblique rod penetrates through a flexible closed bag and is connected with the horizontal rod and the vertical rod to form a tripod structure, and a steel mesh is placed between the vertical rod and the flexible closed bag. The construction method comprises steps that S1, the vertical rod, the horizontal rod and the oblique rodfor steel pipe processing are respectively prepared, the vertical rod, the horizontal rod and the oblique rod are hinged through pins, and the air-cylinder coated cloth is processed into the flexibleclosed bag. The fast die erecting device is advantaged in that fast die erecting in a closed state is realized, a problem that a side vertical mold individual body can not be recycled in the closed wall is solved, enclosure cost is reduced, and roadway enclosure efficiency is improved.